Updated 15 December 2013

"Elswick Pattern" 6-pdr gun under construction at the Elswick Works
Photograph courtesy of Dave Perkins

6-pdr on anti-zepplin HA mounting on submarine D3
D3 was later fitted with a more conventional 6-pdr and often operated without a gun
Photograph from the collection of Dave Perkins and used here by his permission

6-pdr on submarine H2 off La Spezzia following a refit in 1917.  The officer in his shirt-sleeves is a Canadian.
This gun was one of those removed from obsolescent battleships at the beginning of the war for use on patrol craft.  The mounting was manufactured in 1915 by the dockyard at Malta and its extemporized nature is obvious.
Photograph from the collection of Dave Perkins and used here by his permission

Illustration from the official 6-pdr Handbook showing Hotchkiss 6-pdr on Mark IV HA mounting
Note the bar for rapid training

Casing from a 6-pdr round
IWM Photograph MUN 3282

28 May 2008 - Benchmark
15 December 2013 - Added photograph of casing