[2] The first Type 173 Mk 1 registered G-ALBN made its first hovering flight on 3 January 1952 but it tended to fly backwards.

[2] The Royal Air Force issued specification H.150 for a general-purpose transport helicopter with the ability to lift bulky external loads.

[2] In April 1956 orders were placed for 94 helicopters of all three types, prototypes with Leonides Major engines and production aircraft to use Napier Gazelle turboshafts.

[2] The third Type 173 was first hovered on 9 November 1956 but further flights were stopped when engine overheating and transmission failures were experienced during ground rig trials.

[2] The original Royal Air Force order for 22 was increased to 26, and the first Type 192 (later given the service name Belvedere) flew on 5 July 1958.

[2] The prototype Type 173 XF785 was stored at the RAF Museum Cosford until 2002, when it was moved to Kemble for display at the Bristol Aero Collection, until that site closed in May 2012.