THE 456th FIGHTER INTERCEPTOR SQUADRON
THE PROTECTORS OF S. A. C.
Grumman OV-1B "Mohawk"
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History: A one-of-a-kind design, the OV-1 was the first turboprop plane to enter US Army service. It was finally retired as late as 1996, and is one of the most modern warbird in the hands of collectors.
The OV-1 was built as a joint US Army and Marine Corps project for a modern battlefield surveillance aircraft. The Marine Corps pulled out of the project before their prototype could be built, but the US Army began placing its orders late in 1959 for the OV-1A and OV-1B. The -1A and -1B differed in that the -1B variant had an 18 foot side-looking radar mounted under the fuselage and offset to the right. The OV-1B also had an internal camera with in-flight processor and an increased wingspan to cope with the extra equipment. While the plane was slow, its huge triple finned tail and engines mounted on top of the wings gave the Mohawk great maneuverability. To protect against small arms fire from the battlefields over which it kept a watchful eye, the cockpit was armored with an aluminum-alloy floor, flak curtains and bullet-resistant windows.
Experience in Vietnam soon showed that the policy of operating reconnaissance aircraft unarmed was not always wise. In response, a new variant, the JOV-1A, was built with four underwing hard-points for guns and rockets. The OV-1C followed and was similar to the OV-1A, but was equipped to use the new infra-red surveillance systems. The final production version, the OV-1D, had side-loading doors for mounting a variety of electronic intelligence equipment. These served over the Cold War battle lines of Europe with great success.[History by David MacGillivray]
There are examples of each Mohawk variant still airworthy, and they continue to see active service in Argentina. Over its production run, 375 Mohawks of all types were built.
Nicknames: Whispering Death (Vietcong nickname)
Engines: Two 1,400-hp Avco Lycoming T53-L-701 turboprops
Weight: Empty 12,054 lbs., Max Takeoff 18,900 lbs.
Wing Span: 48ft. 0in.
Length: 41ft. 0in.
Height: 12ft. 8in.
Maximum Speed: 370 Knots
Range: 1,011 miles
Number Built: 375
Number Still Airworthy: Approximately 10
The Grumman OV-1 Mohawk
Greg Goebel / Public Domain
The pioneer in the field of battlefield surveillance aircraft was the Grumman "OV-1 Mohawk", a twin-turboprop machine that served with distinction with the US Army for several decades.
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In late 1954, the US Army issued a requirement for a battlefield surveillance and utility aircraft, and in early 1956, the Army met with representatives of six aircraft manufacturers to consider proposals. The proposals were used to generate a final specification, which was kicked upstairs to the Pentagon for approval in the spring of 1956.
At this point, the political wrangling began. The Department of Defense wanted the Army to talk to the US Air Force (USAF) to ensure there was no duplication of missions between the two services. The US Navy, working on behalf of the Marine Corps, also became involved.
While Army officials haggled with their opposite numbers in the other armed services, in June 1956 the Army came up with a final specification for the new aircraft, indicating that it should have twin turboprop engines for combat survivability; carry a crew of a pilot and observer; be capable of short takeoffs and landings on rough airstrips; and be able to fly in bad weather conditions. The Navy also wanted the aircraft to operate from small escort carriers. Although one of the consequences of interservice politics of the time was that the Army was restricted to operating fixed-wing aircraft with an empty weight of less than 2,270 kilograms (5,000 pounds), the limit was waivered in this case.
In March 1957, Grumman Aircraft Corporation was awarded the contract to develop the aircraft, which was given the company designation of "G-134". The contract specified development of nine prototype and evaluation aircraft, with five for the Army to be designated "YAO-1", and four for the Marines to be designated "YOF-1".
The relationship between the services over the G-134 was quarrelsome. The Marines wanted a simple spotter aircraft to replace their old Cessna OE-1 Bird Dogs, and were not interested in the sophisticated sensor payloads that the Army was considering for the G-134. The Marines also wanted the G-134 to have stores pylons to carry weapons, which annoyed the Air Force, which wanted to retain control of the battlefield close-support mission. However, the Navy decided to build a fleet tanker vessel and didn't have the money to buy the Marines a new observation aircraft. The Navy and Marines pulled out of the program in September 1957, much to the relief of the Army. The Army took over the four Marine prototypes; apparently all nine prototypes were assigned the "YAO-1" designation.
The first Grumman YAO-1 performed its initial flight on 14 April 1959 from the Grumman plant at Bethpage, New York, with Grumman chief test pilot Ralph Donnell at the controls. The flight test program went very smoothly, with few major changes required to the basic design. The aircraft proved to be marvelously agile, with a low stalling speed and very good short-field performance.
It was also powerful and fast compared to the piston-engined aircraft previously flown by many Army aviators, and in fact set a number of performance records for its class. The type's high performance would eventually lead to a number of deadly accidents, caused by pilots who became overenthusiastic at the controls. This was not really a fault of the aircraft, which had few handling vices and was extremely strong. Although the YAO-1F was designed for a ten-year service life, fatigue tests demonstrated that it would probably be good for twice that, a tribute to Grumman's tradition of building very rugged aircraft.
The YAO-1 was named the "Mohawk" after the Army's tradition of naming aircraft after American native tribes. There's a little odd story behind the name selection: the Army originally selected "Mohawk" and asked if the company liked the name; Leroy Grumman suggested "Montauk" instead, after a tribe that was native to Long Island, Grumman's home base. The Army wasn't too particular but the paperwork had gone too far to make the change, and so the Army simply suggested that "Montauk" be reserved for the next aircraft Grumman built for the Army. That name would never be used.
Even before the first flight of the prototype, in March 1959 the Mohawk had been ordered into production as the "AO-1AF". It went into US Army service in Germany in 1961 and in Vietnam in September 1962. In that month, the US military services consolidated their aircraft designation schemes, and the YAO-1 and AO-1AF became the "YOV-1A" and "OV-1A" respectively.
The OV-1A carried a KS-61 reconnaissance system built around a KA-30 camera in a bay in the rear fuselage. The camera could pivot from horizon to horizon and could be set to shoot vertically, 15 degrees off the centerline, or 30 degrees off the centerline. Boxy photoflash flare pods could be fitted above the wing roots to provide a total capacity of 52 flares, which were ejected upward to ensure that the flash was above the camera and stayed out of the field of view. One unusual sensor payload was an AN/ADR-6 radiation detector ("radiac"), fitted in the rear fuselage to allow the aircraft to map radiation on a nuclear battlefield. The detector activated a cockpit alarm if radiation levels were high enough to put the crew at risk. The Mohawk was also fitted with a comprehensive suite of radio and navigation gear, as well as an IFF transponder.
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The Mohawk had a bulged cockpit with a snub nose to provide a superlative view for its pilot and observer. In principle, both crew had flight controls, but in practice the right-side flight controls usually weren't fitted. Canopy side panels hinged upward to allow entrance and exit from the cockpit, with a boarding step sliding down from each side of the nose below the panels.
The two flight crew sat in armored Martin-Baker Mark 5 ejection seats, which fired through frangible canopy top panels. Ejection seats were adopted because the Mohawk had big props on either side of the cockpit that blocked a conventional bailout, and the Mohawk was intended to fly operationally at low altitudes, making a "manual" bailout suicidal in any case. It was the first aircraft built specifically for US Army service to have ejection seats. The Mark 5 seats could be fired from zero altitude, but required a minimum flight speed of 185 KPH (100 knots) to be used safely. Improved Mark 5D seats were later fitted that reduced the minimum safe flight speed to 110 KPH (60 knots).
The cockpit floor was 6.4 millimeter (1/4 inch) thick Dural (aluminum / copper / magnesium alloy) plate for protection against small-arms fire; the windshield glass was bullet-resistant and 2.5 centimeters (an inch) thick; and the cockpit could be fitted with flak curtains on the forward and rear walls. Heavy-duty windshield wipers were provided to deal with wet weather.
The Mohawk had tricycle landing gear, with the nose wheel retracting backward and the main gear retracting outward into the wings. The gear was hydraulically activated, with a backup pneumatic system. All the gear had single wheels and the nose wheel was steerable. Low-pressure tires were fitted to heavy-duty struts for rough-field operation, and a small tailskid was fitted to protect the rear fuselage during steep short-field takeoffs.
The YOV-1As had been fitted with Lycoming T53-L-3 turboprops with 715 kW (960 SHP) each. Initial production batches of the OV-1A featured the nearly identical T53-L-3A engine, but later production had the T53-L-7 with 750 kW (1,005 SHP) each. The Mohawk is said to have been the first fixed-wing aircraft to be fitted with the T53, the engine already having been selected for the Bell UH-1 (HU-1) "Huey" helicopter. The engines were mounted on top of the wings, giving them some protection against ground fire, and "toed out" slightly to improve engine-out handling. The exhausts were on top of the nacelles, which would later give the aircraft a degree of protection against man-portable heat-seeking surface-to-air missiles (SAMs). The engines were not "handed", simplifying maintenance and support at some (apparently negligible) cost in maneuverability. They drove three-bladed Hamilton Standard propellers with a diameter of 3.05 meters (10 feet). The propellers were fully reversible to reduce landing roll.
The wings had a 6.5 degree dihedral, and were fitted with large-area flaps and full-span leading-edge slats to reduce takeoff roll. Take-off run was 358 meters (1,175 feet), in contrast to 1,160 meters (3,800 feet) for a Lockheed C-130 Hercules. Although an early G-134 mockup featured a high tee tail, this proved inconvenient for engine-out flight, and a distinctive triple-fin tail scheme was adopted instead.
A hydraulically-operated dive brake was fitted to either side of the rear fuselage behind the wing. Internal fuel capacity was 1,125 liters (297 US gallons) in a single self-sealing fuel tank in the fuselage above the wings, giving the Mohawk an endurance of 2 hours 20 minutes. The tank was part of the aircraft's frame, and it was built very strong, with panels from it subjected to machine-gun fire in tests to ensure survivability.
In operation the Mohawk generally carried a 567 liter (150 US gallon) fuel tank under each wing, giving the aircraft an endurance of 4 hours 30 minutes. Double-size external tanks could be used for ferry flights, but these were rarely used. The OV-1A was designed to be fitted with up to six underwing pylons, as per Marine requirements, but only two were fitted initially in production, to allow it to carry the two external tanks. The aircraft was designed for easy maintenance, with direct access to the majority of systems through panels that could be reached without ladders or work stands. The avionics bays were in the fuselage beneath the wings.
There were minor difference from the YOV-1A prototypes and the OV-1A, such as an improved nosegear strut; deletion of "eyebrow" windows above the windscreen and deletion of small windows behind cockpit side transparencies; addition of a hinged nose cone; and fit of black rubber pneumatic de-icing boots on the leading edges of the flight surfaces. A total of 64 OV-1As were built, with initial deliveries in early 1960 and final deliveries in early 1965.
OV-1B (AO-1BF) / OV-1C (AO-1CF)
The OV-1A was actually produced more or less in parallel with two other variants, the "OV-1B" and the "OV-1C" (originally "AO-1BF" and "AO-1CF" respectively). Essentially, at the outset there were three specialized Mohawk variants, one for daylight observation (the OV-1A); one for radar observation (the OV-1B); and one for infrared observation (the OV-1C).
The prototype OV-1B was modified from one of the nine YOV-1As and performed its first flight on 13 September 1960. The primary enhancement was the addition of the big Motorola "AN/APS-94 Side Looking Airborne Radar (SLAR)", with the radar antenna in a 5.5 meter (18 foot) long, boxy, yaw-stabilized fiberglass pod slung under the right fuselage. The OV-1B retained the optical cameras.
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The Prototype OV-B
The AN/APS-94 SLAR provided an imaging reconnaissance capability in day or night, in any weather. It shot radar signals to either or both sides of the aircraft and recorded the echoes onto photographic film strips, which were automatically developed in flight. A sensor station was installed to allow the operator in the right-hand seat to monitor and control the SLAR. The SLAR also had a "moving target indicator (MTI)" capability to highlight moving vehicles on the imagery. An autopilot and Doppler navigation radar were added to help the aircraft fly nice neat radar mapping patterns, and a VHF data link was installed to allow real-time relay of SLAR data to a ground station. This being the days before digital sensor systems, apparently the datalink simply relayed the analog radar returns to a ground station to be stored on film or by other analog means.
Initially, the airframe configuration of the OV-1B was much the same as that of the OV-1A. However, the leading-edge slats (which had not proven very useful) and airbrakes were deleted in later production batches, and the wingspan was stretched by 1.79 meters (5 feet 10 inches) to help lift the SLAR. Most of the early machines were refitted with the wider-span wing. As with the OV-1A, initial OV-1B production featured T53-L-3A engines, while later production featured T53-L-7 engines. Some OV-1Bs were refitted with Lycoming T53-L-15 turboprops with 860 kW (1,150 SHP) each.
101 OV-1Bs were built, with initial deliveries in the summer of 1960 and final deliveries in the spring of 1965.
Initial OV-1C production examples simply amounted to an OV-1A with an "AN/UAS-4 Red Haze" infrared (IR) sensor system in addition to its optical cameras. The AN/UAS-4 could spot fires, hot truck engines, and other evidence of enemy activities at night, in poor weather, or under jungle canopy. The sensor was originally mounted in the rear fuselage, but was later put in a blister on the belly just behind the wing, along with a panoramic camera and an anti-collision light.
As with the OV-1B, the operator was provided with a sensor control station, and the IR data was recorded on film strips. The AN/UAS-4 was later replaced with the more sensitive "AN/UAS-14", which included a data link to allow reconnaissance data to be transferred to battlefield commanders in real time. The greater sensitivity of the improved sensor allowed operations at higher altitudes, giving more protection against small-arms fire. The OV-1C was also said to have featured a chute to allow the flightcrew to drop messages to field units; it is unclear if other Mohawk variants had this little feature.
Also as with the OV-1B, initial OV-1Cs had airframes similar to those of the OV-1A, with airbrakes, leading-edge slats, and short wings, as well as T53-L-3A engines; and were enhanced in production to long wings with the airbrakes and slats deleted, and T53-L-15 engines. The OV-1C was, however, the first Mohawk variant to be built with air conditioning. The late production machines with the T53-L-15 engines also had "tape"-style dashboard indicators replacing the classic dial indicators; these machines were sometimes called "Super Cs". Late production OV-1Cs had a nose panel for a KA-60 panoramic camera that could take 180 degree pictures in front of the aircraft, and this feature was also retrofitted to older aircraft.
169 OV-1Cs were built, with delivery from early 1961 to late 1969. It was the most numerous Mohawk built.
Early on, there were a number of interesting experiments with the Mohawk. One OV-1B was experimentally fitted with a midair refueling probe for ferry flights, but this scheme was not adopted. Snow ski landing gear was successfully evaluated for the Mohawk, but it was never used operationally. There was even a scheme to fit the Mohawk with water ski landing gear, in response to a Marine request, to allow it to land on calm waters and taxi up to a beach. The concept was successfully tested, but it wasn't used operationally; apparently pilots were not comfortable with the idea of setting an aircraft down on water with the prospect of sinking if taxi speed fell too low, though it is likely some adventurous sorts would have thought water-skiing an aircraft was good fun.
In 1967, Grumman modified two OV-1Bs and two OV-1Cs under the "Southeast Asia Mohawk Requirement (SEAMORE)" program with a substantially improved avionics suite, including improved sensors, navigation and targeting systems, and a radar warning receiver (RWR). They were flown over Southeast Asia during the last years of the Vietnam War, with one lost in action. The SEAMORE program remains a bit mysterious.
The Mohawk had originally been designed to carry a light warload, and the US Army didn't see any reason not to make use of the capability in Vietnam. The Army had Grumman refit a number of OV-1As (including two of the YOV-1A prototypes) and OV-1Cs with all six stores pylons and install a Mark 20 fixed reticle gunsight in the cockpit for the pilot. These modified aircraft were redesignated "JOV-1A" and "JOV-1C". In principle, they could carry:
- XM14 (SUU-12) 12.7 millimeter (0.50 caliber) Browning machine gun pods with 750 rounds each.
- XM18 (SUU-11) 7.62 millimeter (0.30 caliber) General Electric six-barreled "Minigun" Gatling-type gun pods with 1,500 rounds each.
- XM13 40 millimeter automatic grenade launcher pods.
- 7-round LAU-32/A or 19-round LAU-3/A 70 millimeter (2.75 inch) rocket pods.
- 4-round LAU-10/A 127 millimeter (5 inch) Zuni rocket pods.
- 113 kilogram (250 pound) Mark 81, 225 kilogram (500 pound) Mark 82, or 450 kilogram (1,000 pound) Mark 83 general-purpose bombs.
- 450 kilogram (1,000 pound) Mark 79 napalm tanks.
- Sidewinder air-to-air missiles.
Other stores included flares pods, smoke generators, and the M4A supply container. It is unclear if all these stores were actually qualified, and very unlikely that all of them were actually carried in service. It is hard to believe Sidewinders were ever carried operationally.
The actual number of JOV-1A/C conversions is unclear: some sources hint that a number of Mohawks were converted to an armed configuration and not re-designated, and that the JOV-1A/C designation was only given to armed machines with dual controls. A total of 59 JOV-1A/Cs is cited but is a bit untrustworthy.
The Air Force saw the JOV-1A/C as a Army attempt to perform the close support mission, which they insisted was their job and objected loudly. The Army formally changed the name back to OV-1A/C, though they did not remove the pylons or the gunsight. Many of these aircraft would serve in Vietnam, often carrying smoke rockets, and sometimes more lethal stores for "self-defense". The Air Force remained very touchy about the issue, even demanding that Grumman drop company brochures that highlighted the Mohawk's attack capability. In 1965, the Pentagon handed down a directive dictating that the Army would not operate armed fixed-wing aircraft.
Having to support three different versions of the Mohawk was troublesome, and so it was logical to develop one Mohawk version that replace all three variants. The result was the definitive "OV-1D".
The OV-1D had the wider wingspan of the OV-1B; the airbrakes and slats were deleted. It featured T53-L-701 turboprops with 1,045 kW (1,400 SHP) and improved propellers; louvered exhaust suppressors could be fitted to help protect the aircraft from heatseeking missiles. The airframe was reinforced to handle greater weights.
The OV-1D featured three fast-access compartments that allowed an improved AN/AUS-24 IR sensor system and the AN/APS-94 SLAR systems to be easily swapped out. The canoe pod for the SLAR could be bolted on or removed quickly, with a full configuration change taking no more than an hour. Early OV-1Ds featured the AN/APS-94D SLAR, while late machines had the AN/APS-94F SLAR. Both sensor systems used the same cockpit display and control panel.
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Mohawk Photo Flash Pod
Camera systems included the standard panoramic camera in the fuselage, the panoramic camera in the nose added to late-production OV-1Cs, and a new KA-76 "serial frame" camera under the fuselage to provide along-track imagery. Night imagery could be obtained using an electronic photoflash unit carried in a wing pod and driven by a nose windmill on the pod. Flares had proven troublesome to handle in the field, with improperly loaded flares said to have caused accidents in which the entire flare load lit off in the launcher pack. The photoflash pod was also used by older Mohawk variants.
Avionics improvements were added as well, particularly in the form of the "AN/ASN-86 inertial navigation system", which provided accurate all-weather flight guidance. In addition, late production OV-1Ds had a very capable defensive countermeasures suite, including:
- An AN/APR-32(V)2 pulsed-radar RWR.
- An AN/APR-44 continuous wave-RWR.
- An AN/ALQ-136 pulsed-radar electronic jamming module.
- An AN/ALQ-162 continuous wave-radar electronic jamming module.
- M130 chaff-flare dispensers.
- An "AN/ALQ-147 Hot Brick" heat-seeking missile jammer, carried on an underwing pylon. The Hot Brick generated an intermittent thermal signal to cause heat-seeking missiles to lose lock; the pod had its own fuel supply to provide heat. The AN/ALQ-147A(V)1 was a self-contained pod, while the AN/ALQ-147A(V)2 was tacked on to the rear of an external fuel tank.
Early machines had a subset of the countermeasures suite, in particular relying on jamming pods carried on wing pylons.
GRUMMAN OV-1D MOHAWK: _____________________ _________________ _______________________ spec metric english _____________________ _________________ _______________________ wingspan 14.63 meters 48 feet wing area 33.44 sq_meters 360 sq_feet length (no SLAR) 12.5 meters 41 feet length (with SLAR) 13.69 meters 44 feet 11 inches height 3.86 meters 12 feet 8 inches empty weight 5,330 kilograms 11,760 pounds max loaded weight 8,215 kilograms 18,110 pounds maximum speed 490 KPH 305 MPH / 265 KT service ceiling 7,620 meters 25,000 feet range 1,520 kilometers 945 MI / 822 NMI _____________________ _________________ _______________________
Four OV-1Cs were converted to the "YOV-1D" configuration for evaluation in 1968, with 37 new-production machines delivered in 1969 and 1970. 61 OV-1Cs were then upgraded to the OV-1D configuration beginning in 1973, with the last delivered in 1981; followed by the upgrade of 17 OV-1Bs to OV-1D configuration, with deliveries from 1982 into early 1987. That gave a 37 new-build OV-1Ds and 82 upgraded OV-1Ds (including the four YOU-1Ds), for a grand total of 119 OV-1Ds in all.
Apparently the Army had some misgivings about the Mohawk early on, since the fussing over the type with the Marines and the Navy had led to an aircraft that was more complicated and expensive than the Army had originally planned. However, once the machine went into combat the Army decided they'd made the right choice after all.
The Mohawk gave outstanding service in the Vietnam war, providing excellent intelligence on enemy positions and activities. It operated over South Vietnam, Laos, Cambodia, and occasionally even North Vietnam. The Mohawk often flew cooperative missions with US Air Force, Navy, or Marine forces. The Mohawk's ability to operate from forward airstrips and provide real-time intelligence was a great benefit to Army field commanders, permitting immediate artillery or air strikes to be called in on enemy troop movements. It was also occasionally used to parachute supply canisters carried on underwing pylons to combat units in isolated locations.
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The Mohawk In Vietnam
Its agility, ability to fly low, and its relatively quiet turboprop engines allowed it to sneak up on the enemy unannounced, and the enemy is said to have referred to it as the "Whispering Death", though this sounds like marketing hype. Its combat survivability was very good, and its reliability and maintainability were outstanding, with the highest availability rate of any Army aircraft.
The Mohawk's lack of serious offensive armament was troublesome to field commanders, however, because in many cases the Mohawks found concentrations of enemy troops who would be gone by the time strikes could be called in. The field commanders argued at length against the Air Force restriction on armed Army fixed-wing aircraft, but got nowhere. In many cases, the Mohawks were armed anyway.
In 1966, one Mohawk reputedly shot down a North Vietnamese MiG-17 fighter with 70 millimeter unguided rockets. The North Vietnamese pilot made a pass at one of a pair of Mohawks, the other loosed a salvo of rockets at the fighter, and to the surprise of all, managed to hit the MiG. However, one Mohawk was shot down by a North Vietnamese MiG in 1969, evening the score. This was the only Army fixed-wing aircraft loss in air-to-air combat during the war.
A total of 27 Mohawks were lost in combat action in Vietnam, including one destroyed on the ground, and a further 36 were lost in accidents. There is a story that the crew of one shot-up Mohawk ejected, and the aircraft then obligingly crashed into a scrapyard. In 1972, Mohawks began to be transferred to the Army National Guard, but the type still remained in first-line regular Army service for two decades longer.
Several Mohawk modifications also saw service. Since it was designed for the reconnaissance role and could carry sophisticated sensors, it was well suited for modification to the "electronic intelligence (ELINT)" role.
The exact history of the use of the Mohawk as an ELINT platform is a little confusing, with different sources giving different stories. In general, it can be said:
- In the early 1960s a YOV-1A and an OV-1C were fitted with an emitter locating ELINT system and used along the Red Curtain in Europe for a few years under a program designated "Silver Lance". It is unclear if they were given any special designation; some sources hint they were designated "EV-1B" or "EV-1C", but that may have been an informal usage.
- In 1969, as a follow-up, two OV-1Cs were fitted with an improved ELINT system and designated "RV-1C Quick Look"; they may have been originally designated "EV-1C". They were used in West Germany in the 1970s.
- This experiment proving a success, beginning in 1974, 31 OV-1Bs were upgraded to the "RV-1D Quick Look II" configuration, with these machines redelivered beginning in 1977. All their conventional sensors were removed, to be replaced with an AN/ALQ-133 ELINT system, with a boxy antenna pod on a pylon under each outer wing. The ELINT system also included an AN/USQ-61 digital data link to relay intelligence data to ground stations.
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In 1986, the Army initiated a service update program for the Mohawk. One OV-1D was modified with a "glass cockpit", Global Positioning System (GPS) satellite receiver, and other modernized kit, with this machine flying in 1988. Although the Army planned to update the entire fleet to the same configuration, the decision was made to phase out the Mohawk, and that was the end of that.
There were a number of proposals for Mohawk variants that never happened. In 1960, Grumman proposed an "AO-1EF", with the forward fuselage stretched 71 centimeters (28 inches) to accommodate a third seat for a sensor systems operator. The additional space could also be used for cargo. It was to feature fixed seats, replacing the ejection seats, and had an entry door behind the propeller arc. The AO-1EF never went beyond a cockpit mockup.
There were other proposals with different engine fits, including one with T55 turboshafts; one with an auxiliary J85 turbojet in the fuselage; and one with twin J85s driving ducted fans. One particularly adventurous proposal was the "Model 134E" Mohawk, which was to be a "tiltwing" vertical takeoff aircraft with four turboprops, a horizontal tail rotor, and a stretched fuselage to allow it to carry cargo or 11 troops. None of these projects went beyond the paper stage.
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Grumman also came up with a design for an extensively modified Mohawk "Model 134R" with an armored tandem cockpit and built-in gun armament as a "counter insurgency (COIN)" aircraft for the Army's "Light Armed Reconnaissance Aircraft (LARA)" competition, but lost to Rockwell International's OV-10A Bronco. The Marines would adopt the Bronco for the spotting role as a replacement for their Bird Dogs. The Philippines later came up with a request for a COIN aircraft, and Grumman responded with a more conservative proposal to update 20 OV-1Bs to a fully armed standard, while Rockwell proposed the OV-10A. However, the Philippine government came up short on money and the sale never happened.
In the post-Vietnam era, the Mohawk generally operated with the US Army in Germany and South Korea, though it did see limited service in Central America as well. Its final combat service was in 1991 during OPERATION DESERT STORM, the campaign to evict the Iraqis from Kuwait. The last Mohawks in US Army service were withdrawn in the mid-1990s. These aircraft had been used to observe North Korean military activities along the demilitarized zone, and were replaced by De Havilland Canada DASH-7 / Airborne Reconnaissance Low aircraft, the subject of the next chapter.
The Mohawk was also used by civilian organizations. Army Mohawks were flown in missions to support the US Forest Service to spot forest fires and obtain survey data on the spread of tree diseases. In 1980, Oregon Army National Guard Mohawks flew surveillance missions to monitor the eruption of Mount Saint Helens in southwestern Washington state. Army Mohawks also assisted the US Coast Guard, the Civil Air Patrol, and state and local public-safety organizations in search and rescue operations, with the SLAR and IR sensors proving particularly useful in hunting for crashed aircraft in mountainous terrain.
In the early 1970s, the US Geological Survey (USGS) performed large-area mapping missions with an OV-1B fitted with a modified SLAR. The flights were part of a study to determine state water resources, and the aircraft was later used to perform survey missions in Alaska. During the Alaska missions, the aircraft carried emergency floatation gear on the underwing pylons to allow the flightcrew to ditch at sea in an emergency, since ejecting into the frigid Arctic environment would have given little chance of survival. The primary pilots for the USGS OV-1B were a pair of grandmothers who had tired of being secretaries, taken flight lessons, and became topnotch pilots.
The US Environmental Protection Agency (EPA) used an OV-1B and an OV-1C to perform environmental surveys of the areas around nuclear power plants in the early 1970s, and a civilian engineering firm working for the Atomic Energy Commission also obtained an OV-1C to monitor underground atomic tests during 1972. The US National Aeronautics & Space Administration (NASA) used a few Mohawks for aviation technology experiments, including one that was fitted with a small turbojet engine for noise tests.
In a particularly interesting application, in 1973 the US Customs Service received four Army surplus OV-1C Mohawks, along with two ex-Navy Grumman S-2 Tracker ocean patrol aircraft, to hunt drug trafficers. The Mohawks were fitted with a Texas Instruments forward looking infrared (FLIR) camera in a turret under an extended nose. Since the Customs OV-1Cs were sometimes fired on by drug runners there was some thought of arming the Mohawks so they could shoot back, but despite the fact that Customs officers often carry some impressive personal firepower, arming a Customs aircraft was judged against the rules. They were originally flown in Army colors but then acquired a much spiffier white / dark-blue color scheme. The Mohawks were phased out in favor of more modern aircraft in 1986.
A few Mohawks ended up in Navy service, with the Navy performing the weapons qualifications for the JOV-1A/C, and later served at the Test Pilot Training School at Patuxent River in Maryland, which necessarily featured a lot of aircraft that nobody would have ever thought of wearing Navy blue. At least three Mohawks ended up in private hands, and occasionally starred in TV series such as AIRWOLF, with the type's unusual looks making it well suited to playing the "black hat".
The Mohawk's foreign service was limited. Both Germany and France were interested in the Mohawk and performed flight evaluations with it in 1962 and 1963. The French Breguet firm actually obtained a license from Grumman to build it, fitted with more powerful de Havilland Gnome turboprops, but the deal fell through. The first Mohawks in foreign service were actually two OV-1Ds were transferred to Israel in 1974 to support monitoring of the Yom Kippur War cease-fire, to be returned to the US in 1984 and refurbished.
23 US Army surplus Mohawks were provided to Argentina in the early 1990s; the Argentines wanted to obtain 11 more but didn't have the money. At last report, ten of these aircraft were still in service, the rest having either been lost or used as spares hulks. The Argentines evaluated the type with a range of weapons, including locally-built cluster munitions.
MOHAWK VARIANT SUMMARY: ______________________________________________________________________ variant new updates notes ______________________________________________________________________ YAO-1 (YOV-1A) 9 Initial prototypes. OV-1A (AO-1AF) 64 Daylight observation variant. OV-1B (AO-1BF) 101 SLAR variant. OV-1C (AO-1CF) 169 IR reconnaissance variant. OV-1D 37 82 Consolidated sensor variant. JOV-1A - 59? OV-1As & OV-1Cs fitted with armament. RV-1C - 2 Quick Look ELINT machines. RV-1D - 31 Quick Look II ELINT machine. OV-1E - 1 Proto for unproduced modernized variant. ______________________________________________________________________
The Mohawk in Vietnam
In limited warfare, the initial advantage usually lies with the enemy. His knowledge and use of the terrain, especially when clouded by bad weather or darkness, make extremely difficult the task of detecting his activities.
In 1962, the Army OV-1 Mohawk Surveillance system was deployed in South Vietnam to accomplish this detection task. Initially, the Mohawk performed its mission through photographic and visual observation, later adding infrared and radar surveillance. The intelligence thus supplied by the Mohawk system has proven to be a major tactical advantage for both U.S. and RVN (Republic of Vietnam) ground forces and air strike teams.
This report presents a brief description of the Mohawk Surveillance System and its trial-by-combat in Vietnam.
The Mohawk Surveillance System
The Mohawk is a small, two-place, twin-turboprop aircraft capable of STOL operations from unimproved fields. It was produced in three versions:
- OV-1A the basic visual/photographic version, equipped with the KS-61 Photographic System, supplemented by the KA-60 forward-looking panoramic camera. The OV-1A had the capability, day and night, for taking vertical and side-oblique pictures, at any desired scale, from treetop height to 25,000 feet.
- OV-1B employed the AN/APS-94 Side-Looking Airborne Radar (SLAR) System, as well as the KS-61. The SLAR system provided permanent radar imagery of ground targets on both sides of the aircraft's flight path. Two separate films simultaneously recorded fixed and moving target information.
OV-1C was equipped with the AN/AAS-14 Infrared Detection Set, in addition to the KS-61 photo system. The IR sensor measured the temperature difference between a target and its surroundings and presented the results as a permanent thermal map on photographic film.
The Mohawk's bubbled canopy and side hatches, and the short, steep slope of its nose, permitted excellent downward visibility to the side, rear, and front. On all versions, protection from ground fire was provided by armor on the cockpit floor, a bullet-resistant windshield, flak curtains on the forward and aft cockpit bulkheads, and a self-sealing fuel cell. Additional personnel armor kits were also provided for the pilot and observer. Martin-Baker ejection seats permitted emergency egress from the aircraft, at low speeds and minimum altitudes.
The Mohawk's primary role was to detect and monitor the movement of insurgent forces and materiel into South Vietnam, and to perform aerial surveillance and target acquisition within the country itself. The enemy's elusiveness coupled with the region's difficult terrain required the Mohawk to utilize its full range of sensors, and to operate in close coordination with U.S. and RVN forces. Indeed, a number of specialized air-strike operations were developed in Vietnam to take advantage of the rather unique capabilities of the Mohawk Surveillance System.
Photographic surveillance was one of the primary means of daylight reconnaissance in Vietnam, and was performed for both U.S. and RVN tactical elements. Photographic target surveillance missions were normally flown by the OV-1A on a preplanned, priority basis. Typically, a team of two aircraft approached the target area, flying in loose formation to allow freedom for quick maneuvers and provide mutual support. When defensive firepower was required during visual/photo missions, the planes deliver mutually supporting fire, in accordance with the rules of engagement. (Those rules allowed the Mohawk pilot to fire only if fired upon.)
Photographic surveillance, using the KS-61 and KA-60 camera systems, was usually performed by means of the single-pass technique, at altitudes between 500 and 1500 feet. Visual surveillance was normally accomplished using the multiple-random-pass technique. The SLAR and IR Mohawks, being fully equipped for the visual/photographic surveillance mission, were used by the U.S. 1st Infantry and 1st Cavalry Divisions, where OV-1As weren't available.
The OV-1B Mohawk, equipped with side-looking airborne radar (SLAR), was one of the primary means for night detection of vehicular traffic in Southeaset Asia. The OV-1B detected fixed and moving targets on land and along coastal and inland waterways. With this surveillance system, the locations of moving targets were determined, as well as the long-term pattern of land and waterborne traffic in critical areas. The multiple-parallel-pass technique was used to obtain target speed and direction. In other cases, a single pass was flown.
SLAR equipped Mohawks performed surveillance in all but the most severe weather, and were frequently called on to fly missions under completely IFR weather conditions. The altitudes (7000 to 14,000 feet) flown during SLAR missions normally allowed radio line-of-sight between the OV-1B and ground based electronic navigation aids. Operation at these altitudes also minimized the need for evasive tactics due to the threat of enemy ground fire, particularly when operating in the southern regions.
During a mission, the RO-166 Recorder-Processor-Viewer enabled target radar images to be recorded and reported to appropriate agencies by the crew. This inflight spot reporting frequently initiated immediate actions against Vietcong or North Vietnamese activities.
Based on the validity of the targets plotted, the SLAR missions were considered highly successful. Due to the high rate of confirmed hits recorded by strike aircraft, coordinates plotted by the OV-1B were often hit even when there was no visible evidence of enemy activity. On an early SLAR mission, the strike team looked over a flare-illuminated area and reported negative findings. They were, nevertheless, directed to hit the coordinates. The subsequent attack on the area resulted in a secondary explosion, confirming the find and adding to the confidence in the OV-1B system.
The OV-1B also proved its ability to acquire moving targets in the inland areas. The SLAR's recorder-processor-viewer, by providing a permanent image, permitted continuing tracking of a particular target. Vehicles kept under surveillance in this manner were followed to their ultimate destination. When numerous vehicles were tracked to the same location, the area was assumed to be a VC staging area. Such information, coordinated with other collection efforts, then formed the basis for raids by B-52s or other strike aircraft.
As the Vietcong increased their nighttime operations, the need became urgent for airborne surveillance equipment capable of reliably detecting their activities. The OV-1C and its infrared sensor fulfilled this need by detecting heat emissions in areas suspected of being occupied by the VC. The major sources of such emissions were cooking fires and the hot engines of land or waterborne vehicles.
The number and pattern of IR emissions aided in determining the location, strength, and disposition of enemy forces. Such information, supplied in real time by the Mohawk's sensors, often led to immediate action to stem the VC's activities. However, IR data was normally used in conjunction with information from other sources to develop overall Vietcong activity trends. After analysis, these trends were forwarded to operational elements for appropriate action.
To provide the best combination of target detection and image reference, OV-1C missions were flown at altitudes between 1000 and 2000 feet, using the multiple-parallel-pass technique. At these altitudes, the IR sensor was capable of detecting high background contrast emissions, even through the jungle growth. If the mission objective was verification of target information developed by other means, the Mohawk was flown at its best IR imaging altitude....generally, between 500 and 1000 feet.
The OV-1C Mohawk and its IR system proved quite effective and reliable in acquiring targets for air strike teams. A good example was the support given Marine forces in the Chu Lai area. The Mohawk flew five missions for the Marines; during four of them the aircraft acquired and made inflight reports on 23 targets. At the start of the Mohawk's operations, the Marines, being relatively unfamiliar with the aircraft's capabilities, had no strike aircraft ready for immediate response. However, they soon came to rely on the Mohawk's reports, releasing strike aircraft soon after a target was acquired. On another flight, the OV-1C located Vietcong units in two positions. These targets were reported to the ground control unit, which then requested naval gunfire on the VC positions.
An unexpected benefit resulting from Mohawk IR operations was a lowering of Vietcong morale. The best IR returns were being received by OV-1Cs operating in the southern delta regions of South Vietnam, where the jungle canopy was less dense than in the central highlands. The subsequent decrease in IR returns, coupled with the fact that IR operations were conducted at night, led to the belief, later confirmed, that the VC had been forced to substantially curtail their cooking and, therefore, were eating less hot food. Prisoner interrogation indicated that the one daily hot meal was being eaten during the day, in an attempt to escape IR detection.
In this operation, the OV-1B Mohawk was used as the sensor aircraft. Flying at an altitude suitable for SLAR surveillance (typically, around 7500 feet), the aircraft patrolled along known or suspected enemy traffic arteries in the Mekong Delta region. Any moving target acquired by the radar was displayed to the observer in the Mohawk by the inflight processor-viewer. Because of the curfew in effect during the hours of darkness, any movement detected was considered to be enemy.
In Operation Firefly, the observer fixed the target's position and transmitted it to an alerted helicopter unit. Armed UH-1Bs were then directed to the area, where they conducted the strike, with a spotlight-equipped UH-1B providing target illumination.
The ability of the OV-1B to "see without being seen" and to operate quietly during these operations was a big advantage, because of the enemy's well-known ability to disperse rapidly under cover of darkness and terrain.
The purpose of this operation was to destroy infiltration shipping along the South Vietnamese coast. On a typical mission, the OV-1B Mohawk acquired targets by flying parallel to the coastline. Once a target was acquired by the SLAR, its position was reported to the Navy's Coastal Surveillance Center. At the Center, the decision was made regarding the proper course of action...interception by Swift-type boats, destruction by naval gunfire, or destruction by attack aircraft.
OV-1B surveillance of the many waterways of the Mekong Delta was the object of this operation. Targets acquired by the Mohawk were attacked by Swift-type boats.
The objective of this operation was to interdict the movement of enemy troops, equipment, and supplies from neighboring countries into South Vietnam. The Mohawk's full range of sensors were utilized in Tiger Hound, with great effect. The prime sensor employed was the OV-1B's SLAR, owing to its capability to detect and plot moving targets at night along the various infiltration routes.
On one occasion, after initial detection by an OV-1B, three targets were located by a "C" model. The next day, after intensively searching for the most likely parking areas, an excellently camouflaged convoy of "a few" trucks were located by an OV-1A. Air Force strike aircraft were called in. On their first pass, the near miss of their bombs blasted off enough camouflage to expose several trucks. Upon completion of the strike, forty trucks were left burning or destroyed.
This operations was similar to Tiger Hound, except that only the OV-1B and its side-looking radar were utilized.
Traffic Cop/Sea Dragon
This operation...the detection of waterborne vehicles moving along the coast...was companion to Tally Ho. It differed only in that detected targets were reported to the Navy, which then attacked with surface vessels.
A part of the major operation Rolling Thunder, which encompassed air strikes against reported targets, Night Hawk is a tactic that made use of the SLAR equipped OV-1B, a command and control aircraft, and strike aircraft to seek out and destroy enemy cargo vehicles. In this operation, near-real-time target acquisition information from the OV-1B was relayed to the C&C aircraft, which, in turn, vectored the strike aircraft to the target. This team effort accounted for numerous vehicles, including trucks and motorized barges.
OV-1 Chronology In Southeast Asia
Sept '62 Initial deployment of JOV-1Cs (armed OV-1Cs, without IR sensors); assigned to 23rd SWAD (Special Warfare Aviation Detachment), Nha Trang, Vietnam.
July '63 ACTIV (Army Concept Team in Vietnam) evaluation found the Mohawk especially well suited for the COIN role, citing its speed, range, speed-noise, maneuverability, endurance, survivability, etc.
Dec '64 New Mohawk unit, 4th ASTA (Aerial Surveillance and Target Acquisition) Platoon formed at Ft. Bragg, N.C., and deployed to Vietnam, with OV-1Bs and Cs.
Jan '65 23 SWAD and 4th ASTA combined, resulting in formation of 73rd Aviation Company, Vung Tau.
Sept-Nov '65 Three additional Mohawk units deployed to Vietnam:
- 1st Cav ASTA Platoon (OV-1Bs and Cs), An Khe;
- 1st Infantry Div ASTA Platoon (OV-1Bs and Cs), Phu Loi;
- 20th ASTA Platoon (OV-1As, Bs, and Cs), Hue Phu Bai.
June '66 20th ASTA expanded into new 131st Aviation Company, Hue Phu Bai.
What we have learned
The fact that effective, routine operations, such as those just described, could be built around the OV-1 surveillance system testified to the soundness of the Mohawk concept...to combine in a modern, fieldworthy airframe an unprecedented electronic/photographic surveillance capability. The operational know-how gained with this system in Vietnam was being used to improve the capabilities of future Mohawk versions for performing a wider range of limited warfare roles.
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