 Bristol produced three designs, the Type 191 to meet the Royal Navy requirement, Type 192 for the Royal Air Force and the Type 193 to be built in Canada for the Royal Canadian Navy.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.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.