After the Javelin Halford’s next new and radical design was the Rapier which Montague Napier referred to as his ‘H-Engine’. The E93 was a 16-cylinder air-cooled, supercharged engine which could produce 300 bhp at 3,500 rpm. This compact engine had a 7:1 compresson ratio and push rod- operated overhead valves.
The Rapier I engine first flew on 11th July 1929 in the prototype De Havilland DH77 experimental light interceptor monoplane fighter. This was an attempt by DH to enter the military aircraft field. It had a good climb rate and a top speed of 200 mph however, after no RAF interest was received the DH77 was used to flight test the Rapier II.
The Rapier II and later E100 Rapier V was used in the Fairey Seafox bi-seaplane which saw use as a catapult launched ‘fleet spotter’ by the Fleet Air Arm. These aircraft were used during WWII with one in particular being flown by Lt Lewin from HMS Ajax spotted targets for Royal Navy cruisers which resulted in the scuttling of the Graf Spee off the River Plate. Four Rapiers were later used in the transatlantic Mercury flying boat which was piggy backed on a ‘mother’ flying boat named Maia. This was the ingenious Short-Mayo Composite pair of flying boats used to deliver a heavy payload of Royal Mail to the USA. The first in-flight separation took place on 6th February 1938 and the pair went into regular service. This included Mercury achieving a 6,045 mile non-stop run from the Firth of Tay to the Orange River in South Africa setting a new world record for seaplanes.