After World War II the Air Ministry issued specifications for a wide variety of rocket engines, both liquid and solid-fuelled.

Fuel and oxidiser were pumped by a single shaft turbo-pump driven by super-heated steam, generated by catalysing HTP.

From 1956 Double Scorpion engines were fitted experimentally to three Canberra light bombers, to improve high altitude performance.

[5][6][7][8] The Double Scorpion was also considered for use in the English Electric P.1A interceptor (which gave rise to the Lightning) and Aerojet General was chosen for projected United States production.

[9] A sectioned Napier Double Scorpion engine is on display at the Royal Air Force Museum London.