NBMR-4 / NBMR-22 V/STOL Tactical Transport
(NATO Basic Military Requirement)

NBMR.4 Tactical V/STOL transport [1962]
UK	B.A.C.	224
UK	De Havilland	129
UK	English Electric	P.36
UK	English Electric	P.41
UK	English Electric	P.44
USA	L.T.V.	XC-142A
France	Breguet	941
Canada	De Havilland of Canada	DHC-4 Caribou
NBMR.22 V/STOL transport
UK	B.A.C.	Bristol 208
UK	B.A.C.	P.43
UK	Hawker Siddeley	Armstrong Whitworth 681
Italy	Fiat	G.222
Germany	Dornier	DO 31

At least by 1960 it was increasingly clear that a Soviet nuclear attack could close NATO airfields, and destroy its nuclear facilities and the high-performance aircraft, giving the Soviets air superiority from the outset of the war. This required NATO to develop aircraft that could take off from rough unprepared airstrips, and but obviously there must be some aircraft to take the necessary equipment, ammunition and petrol to these advanced fields. After study of their needs, the military authorities of NATO defined three general types of V/STOL aircraft answering to the NBMR (NATO Basic Military Requirement) 3, 4 and 22. Work groups were created to examine the possibility of manufacture of joint prototypes. The NATO 1961 VSTOL competition was in two parts: submissions for a general-purpose transport have to be made by 15 November 1961; submissions for a strike and reconnaissance aircraft must be completed by 31 December 1961.

To fully realize the potential of VTOL transports, they would be required to operate routinely to low visibility minimum under Instrument Flight Rules (IFR) and to minimize ground and air maneuver time, fuel, airspace and noise. These requirements clearly indicated the landing approach to be the most critical flight condition for these aircraft. Further, research had shown the approach phase to be the most demanding in terms of pilot workload and indicated that a number of unresolved questions existed.

The Ad Hoc Mixed Working Group [AHMWG] on V/STOL medium range transport aircraft AC/170 was created on June 24, 1960 to study the development and coordinated production of a transport aircraft of the V/STOL type with a medium radius of action, with the mandate formulated in the document AC/74-D/454. It has with the founded departure its work on the needs formulated by the military authorities of NATO in the NBMR-4 promulgated on 29 July 1960. One finds the same participating countries as for the group AC/169 Ad hoc mixed working group on V/STOL strike reconnaissance aircraft : Germany, Belgium, Canada, France, Italy, Netherlands, the United Kingdom and the United States (Greece in 1961).

Two aircraft competing for Ministry of Aviation [MoA] sponsorship in the UK were the Bristol 208 (British Aircraft Corporation) and the Armstrong Whitworth 681 (Hawker Siddeley Aviation). Both aircraft were to be powered by four Bristol Siddeley lift/thrust engines; with four separate nacelles as on a Boeing 707, though control problems would be eased by grouping the engines well inboard. If the powerplant was to be the Pegasus, both designs had gross weights in the neighborhood of 80,0001b, and speeds comparable with current jetliners (they would probably be over-powered in the cruise regime). These aircraft would not be capable of true VTOL until more powerful engines become available, or until batteries of specialized lift engines were added.

Under NBMR-4 The group started by defining the characteristics operational and technical specifications of theplane. For the second time, the group asked the aircraft industry to submit projects. Six NATO countries submitted 25 studies which were examined by a project assessment group. Five were reserved for a more thorough evaluation (AC/170-D/31). In spite of the quality of the projects presented, the countries could not agree on any of the aircraft proposed. The group submitted a report by document AC/170-D/32 of 30 November 1962, where they formulates negative conclusions on the prospects for coordinated manufacture. The Committee of Armaments took of it note (AC/74-D/722) and transmitted to the Council (CM (62) 157), which took of it note in its turn on January 16, 1963 (CR (63) 2, point II).

Under NBMR-22, in November 1962, the Committee of Armaments widened the mandate of group AC/170 to allow study of the realization of one prototype STOL transport aircraft with a shorter operating range (500 km), for startup around 1964-1965. It was renamed on this occasion the "Ad hoc mixed Work group on the transport aircraft V/STOL and STOL". Its documents were distributed from this moment under special dimension AC/170 (STOL). The study was launched on the basis of NBMR-22. It appeared that only one country, France, had a firm need for this type of plane. The group submitted its conclusions in a report to the Committee dated March 6, 1963 Armaments (AC/74-D/741). The Committee noted the report and decided not to take any new study with subject of the NBMR-22 within the framework of group AC/170, but at the request of France the group was not dissolved [AC/74-R/128, point III. 82 AC/74-D/714 (Revised) and AC/74-R/122, point III].

In September 1966, it was attached to Group NATO on the armament of air forces (AC/170-D/33). With this date, them military authorities did not plan any more to resume the study of the NBMR-4 and 22. As it was definitively removed at the same time as the AC/169 in April 1967.