The Westland Wasp was a British small first-generation, gas-turbine powered, shipboard anti-submarine helicopter. Produced by Westland Helicopters, it came from the same P.531 programme as the British Army Westland Scout, and was based on the earlier piston-engined Saunders-Roe Skeeter. It fulfilled the requirement of the Royal Navy for a helicopter small enough to land on the deck of a frigate and carry a useful load of two homing torpedoes.
Design and development
The increasing speed and attack range of the submarine threat, and the increased range at which this threat could be detected led to a Royal Navy requirement for a "Manned Torpedo-Carrying Helicopter" (MATCH). Contemporary shipboard weapons did not have the necessary range, therefore MATCH was in essence a stand-off weapon with the helicopter carrying the torpedo or other weapon to the target and being instructed when and where to drop it. Unlike the larger Wessex, the Wasp carried no sonar of it own, and was limited strictly to working in partnership with its parent ship, other ships or other ASW units.
The first prototype Saro P.531 flew on 20 July 1958, with the prototypes being subject to detailed testing by the Royal Navy, including the evaluation of several different undercarriage layouts, before settling on the definitive arrangement. An order for a pre-production batch of two "Sea Scouts" was placed in September 1961. The first flight of the two pre-production Wasp took place on 28 October 1962. Full production soon commenced, 98 in total being procured for the RN. The Wasp successfully exported to Brazil, the Netherlands, Indonesia, Malaysia, New Zealand and South Africa. 133 aircraft were built in total.
Wasp was essentially a navalised Scout, indeed it was originally to be called the Sea Scout, and differed mainly in design details. It had a unique 4-wheeled castering undercarriage that allowed the aircraft to be manoeuvred on small, pitching flightdecks. The Wasp had the ability of "negative pitch" from the rotor-blades which enabled the aircraft to "adhere" to the deck until the lashings were attached. Additional fuel tankage was installed in the cabin floor and both the tail boom and main rotor blades were foldable to allow stowage in the small hangars fitted to the first generation helicopter-carrying escorts. It was fitted with a winch above the starboard rear door, and also had the capacity to carry under-slung loads from the semi automatic cargo release unit mounted under the fuselage. With a crew of 2 (Pilot and Missile Aimer/Aircrewman) and the capacity to seat 3 passengers Wasp was useful for short-range transport missions, and for casualty evacuation with room for one stretcher fitted across the rear cabin area.
Later modifications included the ability to carry the Nord SS.11 wire-guided missile, with the fitting of the Aimers sight in the left cockpit roof and the installation of large inflatable emergency floats in sponsons on either side of the cabin to prevent capsizing of the top-heavy aircraft in the event of ditching. The SS.11 had limited range to target small surface targets such as patrol boats or shore positions and this was later replaced by the AS.12, which effectively had double the range.
Crew: One pilot, one Aircrewman
Capacity: up to four passengers
Length: inc rotor 40 ft 4 in (12.30 m )
Rotor diameter: 32 ft 3 in (9.83 m)
Height: 8 ft 11 in (2.72 m)
Disc area: 816.9 ft² (75.9 m²)
Empty weight: 3,452 lb (1,569 kg)
Max takeoff weight: 5,500 lb (2,500 kg)
Powerplant: 1 × Rolls-Royce Nimbus 103 turboshaft, 1,050 shp  (783 kW)
Maximum speed: 120 mph (104 knots, 193 km/h)
Cruise speed: 110 mph (96 knots, 177 km/h)
Range: 303 miles (263 NM, 488 km)
Service ceiling: 12,200 ft (3,720 m)
Rate of climb: 1,440 ft/min (7.3 m/s)
Disc loading: 6.75 lb/ft² (33 kg/m²)
Power/mass: 0.19 hp/lb (0.31 kW/kg)
Naval: 2 x Mk 44 or 1 x Mk 46 torpedo or 2 x Mk 44 depth charges or WE.177 600lb Nuclear Depth Bomb.
Attack: 4 x SS-11 replaced by 2 x AS.12 missiles.
General: GPMG, 4.5 Flares, Smoke/flame floats.