Three (C36, C37 and C38) had been sent to Hong Kong in 1911 and during the war the remainder were mainly used for coastal defence, based at the east coast ports of Leith, Harwich, Hartlepool, Grimsby and Dover, some operating with Q-ships which were decoying U-boats.

Packed with explosives it was blown up in an attempt to destroy a viaduct, for which her commander Lieutenant Richard Sandford was awarded the Victoria Cross.

Four operated in the Baltic Sea, based at Tallinn as part of the blockade of Germany trying to prevent the import of iron ore from Sweden.

They were sent there in September 1915 via a tortuous route — towed around the North Cape to Arkhangelsk and taken by barge to Kronstadt.

Three of these boats were destroyed (along with the British E-class submarines E1, E8, E9, E19) outside Helsinki in 1918 to prevent capture by German troops of the Baltic Sea Division who had landed nearby.