A single-engined tractor biplane, the Wagtail was a failure owing to the unreliability of its engine, only five being built.
Westland's design team, led by Robert Bruce, the Company's manager and Arthur Davenport, Chief Draughtsman, came up with a design for a small single bay biplane, powered (like the other competitors for the Specification, the BAT Bantam and the Sopwith Snail) by the 170 hp (127 kW) ABC Wasp radial engine.
The Wagtail was of conventional wood and fabric construction, with the upper wing centre-section having a large cut-out to improve the pilot's view, and carrying an armament of two Vickers machine guns mounted over the nose.
[6] Despite this, two further Wagtails were ordered in 1920, as testbeds for the new 150 hp (112 kW) Armstrong Siddeley Lynx radial.
These two aircraft, which had a shorter nose to compensate for the heavier engine, were delivered in 1921 and remained in use until August 1922.