In September 1916, Lieut Commander John Porte, Commander at RNAS Felixstowe and designer of the Felixstowe series of flying boats, suggested using specially designed lighters to extend the range of his flying boats.
Each lighter would carry one flying boat and it would be partly submersible to allow the aeroplane to be floated on and off. Once floated off, the flying boat could take off in the normal way. The lighters would be towed behind destroyers at speeds of up to 30 knots.
Four prototypes were ordered from Thornycroft of Southhampton, testing beginning in June 1917. The trials proved very successful and 25 production lighters were ordered. This was later increased to 50, but due to the end of the war only 32 were built. The production versions were built by the Royal Engineers at Richborough, Kent, the first being delivered in May 1918.
From March 1918 the lighter mounted flying boats carried out reconnaissance flights off the German coast. A flying off platform could also be mounted on the lighters from which a small fighter could take off.
On 11 August 1918, a Sopwith Camel 2F1, taking off from a lighter and flown by Lieut S. D. Culley, destroyed Zeppelin L53 at 18,700 ft off Terschelling.
Admiralty Seaplane Lighter H21 was rescued from the Thames mud in 1996 and is now at the Fleet Air Arm Museum.
Felixstowe F2A. J. M. Bruce. Albatros Productions Ltd ISBN 1-902207-24-6.http://navalairhistory.com/2012/03/14/flying-boat-lighter-stunts/http://www.dailymail.co.uk/news/article-1361523/Worlds-oldest-aircraft-carrier-discovered-rusting-River-Thames.html