Prior to the conflict of World War One, the submarine was mainly seen as a tool of coastal defence,and to aid fleets of naval ships, protecting their flanks.   Germany and Austria were to prove that they were a supreme offensive weapon and the Allies had to change operations and tactics to counteract this.

In the early 20th Century, Submarines had been occasional vistors to Cork,as part of visiting fleets on manouveres, and for demonstrations, including the ill-fated HMS A5 . There were no submarines stationed here before 1917.

The unrestricted u-boat offensive of 1917 was proving catastrophic to England and her Allies. Vice -Admiral Lewis Bayley, received critical reports from the Admiralty complaining that u-boats were rounding the north and West coasts of Ireland with impunity.   This saw the advent of the defence of the 'hunter-killer' submarine. patrolling Irish waters, patrolling singly, shadowing commercial shippping, in the hope of spotting an enemy submarine and attacking it.

HMS L1 Vulcan Flotilla, Dec 1917.

Two flotillas were established in Ireland. The Platypus and Vulcan flotillas, named after the submarine depot ships HMS Platypus and HMS Vulcan , which provided supplies, mobile workshops, and accomodation to resting submariners.

Submarine Depot Ship HMS Vulcan

During 1918 another depot ship HMS Ambrose was also stationed here to assist. This became for a time a combined Vulcan/Ambrose Flotilla . Thse flotillas were mobile, and at various stages were based in Queenstown (Cobh), Co. Cork, Berehaven Co. Cork, Lough Swilly, Co.Donegal, and Killybegs Co Donegal.

Submarine Depot Ship HMS Ambrose

Twenty three Royal Navy submarines were stationed in Ireland over the course of World War One. By November 1918 There were five, all stationed in Donegal.

HMS D7 Platypus Flotilla, 1917.

List of RN Submarines stationed in Ireland during WW1