The First to Go Up and Down
The Hawker Siddeley Kestrel was not a naval aircraft. But the British airplane had a profound impact on U.S. naval aviation: It was the progenitor of the widely flown Harrier-series vertical/short takeoff and landing (VSTOL) aircraft. Indeed, the U.S. Marine Corps has been the largest user of these highly successful VSTOL planes.
The aircraft was initiated by Hawker Siddeley in 1957 as a private venture and given the company designation P.1127.1 Many previous efforts had been made to develop VSTOL combat aircraft, including the U.S. Navy-sponsored Lockheed XFV-1 and Convair XF2Y-1 Pogo.
But the Kestrel offered the promise of a practical VSTOL configuration, employing a vectored-thrust engine to achieve vertical flight. The Royal Air Force placed an order for six Kestrel prototypes, the first of which rose vertically for the first time on 21 October 1960 and flew its first horizontal takeoff and conventional flight on 13 March 1961. The six prototypes were provided with progressively uprated versions of the Bristol Siddeley Pegasus engine as well as aerodynamic changes.
One of these aircraft flew trials from the large carrier Ark Royal in February 1963. Twelve landings and takeoffs were made while the ship was under way; half of the flights were made in the vertical takeoff mode.
Nine aircraft were then produced for a British-West German-U.S. evaluation squadron. The first of the nine flew on 7 March 1964, with the RAF designation F.(G.A.) Mark 1, indicating Fighter (Ground Attack). The Tripartite Evaluation Squadron was assigned eight aircraft (one had crashed) and ten pilots-four from the Royal Air Force, two from the West German Air Force, one from the U.S. Air Force, two from the U.S. Army, and one from the U.S. Navy. Significantly, in view of the future of VSTOL aircraft, no U.S. Marine Corps pilots served in the squadron.
The Kestrel evaluation squadron operated from 15 October 1964 until 30 November 1965 and its aircraft made 938 flights during that period, operating from British and other NATO bases.
These evaluation aircraft were powered by the BS.53 Pegasus vectored-thrust turbofan, rated at 15,2000 pounds static thrust. The aircraft had a vertical takeoff gross weight of 12,400 pounds and a maximum short-takeoff gross weight of 15,500 pounds. Their cruising speed was Mach 0.85 (645 mph) at sea level with a dash speed of Mach 0.87. Two wing store stations could carry up to 1,000 pounds each in the short-takeoff mode.
With the disbanding of the tripartite squadron, six of the aircraft were shipped to the United States, where they underwent further evaluation by the Air Force, Navy, and Marine Corps. In U.S. service, the aircraft were designated XV-6A.2 During the 3.5-month evaluation in 1966, the six flew a total of 374 sorties. The Navy's portion of the trials included flights from the aircraft carrier Independence (CV-62) and amphibious landing ship Raleigh (LPD-1). Although these trials, as well as operations on board the British carrier Bulwark in 1966, proved that the Kestrel could operate from ships, the Royal Navy did not believe that VSTOL aircraft had been developed to the point that offered significant advantages over conventional fixed-wing aircraft. Catapults would still be required to launch the VSTOL aircraft, because takeoff with a combat load would not be possible in the vertical mode. Also, the downward vector of the exhausts could cause thermal problems during catapult launches and other operations.
The RAF did procure the Kestrel-derivative Harrier GR.1, a fighter-ground-attack aircraft with a level-flight speed of Mach 0.98. It could be fitted with two 30-mm gun pods or up to five 1,000-pound bombs or equivalent loads of drop tanks and rockets in the short takeoff mode. (A proposed advanced VSTOL fighter derivative-the P.1154-was to be a Mach 1.5 aircraft developed in response to a NATO requirement, but it was cancelled in 1965.)
The first RAF Harrier GR.1 flew on 31 August 1966 but it was almost three years before the RAF took delivery of its first service Harrier in April 1969. Also that year, Minister for the Navy David Owen publicly mentioned the possibility of RAF Harriers operating from Royal Navy commando ships-amphibious helicopter carriers-as well as from a new class of ASW cruiser-carriers being developed.
Owen's statement led Hawker Siddeley to immediately propose a naval variant of the Harrier-the Sea Harrier-which was not taken up at the time. However, by 1970-71 the cruiser-carrier studies had evolved into a ship of 18,750 tons standard displacement. The ships were referred to in this period as "through-deck cruisers," as the Admiralty eschewed the term "carrier" for political reasons. Some journalists promptly dubbed the concept the "Harrier carrier."
The lead ship-to be named Invincible-was ordered from the Vickers yard at Barrow-in-Furness on 17 April 1973. By that time the Admiralty had established a requirement for ship-based Harriers, but procurement could not be pursued because of the economic crisis that followed the October 1973 Yom Kippur War when Arab states raised oil prices. The Sea Harrier, distinguished by having radar, a raised cockpit, and corrosion-resistant structure, flew for the first time on 20 August 1978, and deliveries to the Royal Navy began in June 1979. Thirty-four FRS.1 aircraft were ordered, enough for a transition-conversion unit and three fleet squadrons, one for each of the Invincible-class ships that were built. At the time a significant debate arose over whether the RAF should provide Harriers for the carriers or control all of the planes, whether flown by RAF or RN pilots.3
(Ironically, all RAF and navy Harrier activities would be combined in the Joint Force Harrier in 2000 to control all Harriers when deployed overseas, whether ashore or on carriers.)4
Meanwhile, the U.S. Marine Corps showed belated interest in the Kestrel-Harrier concept. In 1968, Marine Colonel Thomas H. Miller Jr. and Lieutenant Colonel Clarence M. Baker were sent to Britain to fly the Harrier GR.1. Based on their evaluation, on 27 October 1969, the U.S. Navy and the Ministry of Defence executed a memorandum of agreement for the Harrier to be procured for the Marine Corps with an initial delivery of 12 aircraft in January 1971.
For U.S. service the Harrier GR.1 was provided with a more powerful engine and given the designation AV-8A Harrier. The Marine Corps acquired 102 single-seat AV-8A and 8 two-seat TAV-8A Harriers. These were succeeded in Marine service by the improved AV-8B, with 262 single-seat and 21 two-seat (TAV-8B) variants acquired.
The U.S. Navy briefly evaluated the Harrier as a ship-based aircraft in the early 1970s. During Admiral Elmo R. Zumwalt's tenure as Chief of Naval Operations, the concept of the sea control ship (SCS) was developed. This was to be primarily an antisubmarine warfare ship to escort convoys, amphibious groups, and underway replenishment groups in situations when a larger aircraft carrier was not available. The SCS was initiated under the rubric "air capable ship" for the ASW role. The design evolved into a small aircraft carrier and in 1973-74 was enlarged, becoming a ship of 17,000 tons full-load displacement with a length of 670 feet and a speed of 25 knots. It was to operate 16 ASW helicopters and 5 Harrier-type VSTOL aircraft, the latter to a provide limited air-defense capability.
The SCS concept was tested at sea with the amphibious ship Guam (LPH-9) from January 1972 to April 1974. The 10,700-ton helicopter carrier embarked a squadron of SH-3G (later SH-3H) Sea Kings and operated a small number of AV-8A Harriers during the tests. Although the tests were successful and the program was endorsed by Secretary of Defense James Schlesinger, the rising cost estimates for the SCS program and, after Zumwalt retired in 1974, opposition from the "big carrier" community, led by CNO Admiral James Holloway III, prompted the rapid demise of the SCS concept and all Navy interest in the Harrier.
Beginning with the company-funded P.1127 prototypes, a total of 828 VSTOL aircraft of the P.1127 "family" have been produced, with almost half of that number built for the U.S. Marine Corps. The other aircraft have been flown by Britain, India, Italy, Spain, and Thailand, with the U.S. Marine Corps (in Iraq and Afghanistan) and the Royal Air Force and Royal Navy (in the Falklands) proving the combat efficacy of these pioneer VSTOL aircraft.
1. The most detailed published account of the Kestrel-Harrier development is Francis K. Mason's Harrier (Cambridge, U.K.: Patrick Stephens Ltd., 1981). The U.S. side of the Kestrel-Harrier story is told in Lon O. Nordeen, Harrier II: Validating V/STOL (Annapolis, MD: Naval Institute Press, 2006).
2. In U.S. designations, the letter V of XV-6A is one of six vehicle-type letters listed in Department of Defense, Model Designation of Military Aerospace Vehicles DOD 4120 (Washington, D.C.: various editions). The others are:
Q Unmanned Aerial Vehicle (UAV)
Z Lighter-than-Air (LTA)
The prefix letter X indicates an experimental vehicle.
3. In the event, a total of 57 Sea Harrier FRS.1 aircraft were produced for the Royal Navy. All have now been retired from British service.
4. See N. Polmar, "Royal Navy: Back to the Past," U.S. Naval Institute Proceedings (July 2009), pp. 88-89.