Upon its review of Armstrong Whitworth's proposal, Imperial Airways opted to order it into production before a prototype had even been assembled, much less flown.

Flying testing revealed only minor difficulties, many of which were rapidly resolved, enabling the aircraft to receive a certificate of airworthiness only three months later.

Other requirements of Imperial Airways' specification include the ability to carry at least nine passengers, along with a crew of three and a payload of freight/mail across a distance of 400 mi (640 km), in addition to a cruising speed of 115 mph (185 km/h) at 9,000 ft (2,740 m).

[2] The basic concept represented a major departure from the preceding Argosy, featuring wing-mounted engines and a relatively streamlined fuselage.

Internal studies, which included considerable use of wind tunnels, found that the proposed airliner would generate 340 lb of parasitic drag, less than half that of the Argosy.

One relatively minor criticism, but still within acceptable margins, was the occasional instance of rudder over-correction and oscillation: this was improved via the addition of what Armstrong Whitworth claimed to be the world's first spring tab.

[5] The prototype was flown to Croydon Airport for customer acceptance trials with Imperial Airways, the airline being reportedly entirely satisfied by its performance.

Armstrong Whitworth was allegedly embarrassed by the incident and renamed the third production machine (G-ABTI, Arethusa) as Atalanta, apparently in the hope that nobody would notice the substitution.

[12] The aircraft was powered by a total of four supercharged Armstrong Siddeley Serval III ten-cylinder radial engines, each capable of providing up to 340 hp (250 kW).

[10] They were mounted upon a tubular framework attached to the forward spar of the wing, which was protected from a potential engine fire by a fire-proof bulkhead.

[11] The cockpit, which was crewed by a pair of pilots and a radio operator, was unusually large; immediately behind it was a compartment intended to accommodate up to one tonne of air mail.

[15] Particular attention was paid to the air conditioning systems due to the type's envisioned frequent use within relatively hot climates.

[23] During March 1941, they were impressed into use by the Royal Air Force (RAF) in India, where they were used to ferry reinforcements to Iraq in response to the Rashid Ali uprising.

[21] During December 1941, shortly following Japan's entry into the war, the fleet was handed over to the Indian Air Force for use on coastal reconnaissance duties, armed with a single .303 in (7.7 mm) machine gun operated by the navigator.