The sub is HMS M2, one of three of the 'M' class, which was originally built as a submarine monitor, mounting a battleship's 12 inch gun. It was launched in 1919.
The 'M' class were large submarines for their time, being around 300ft long and displacing 2000 tons submerged.
In 1927, HMS M2 was converted to a 'submarine aircraft carrier' by removing the gun and replacing it with the watertight hangar.
A year later, the pneumatic catapult was fitted, allowing the aircraft to be launched directly from the deck.
The aircraft is a Parnall Peto, powered by an Armstrong-Siddeley Mongoose 5 cyl radial and was specially designed for the M2.
The sub was lost in January 1932 in an accident which was thought to have been caused by the hangar door being prematurely opened.
All 60 crew were killed.
She lies in about 100ft of water at West Bay, Dorset and is a popular dive-site.
EDIT: Oh dear, everybody got in before my one-finger typing could get me there. Pish!
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Last edited by Stanwell; 22nd Jun 2016 at 16:27.