HMS A7 (Lt. G M Welman) sailed from Devonport on 16 January 1914 for exercises off Plymouth with the depot ship HMS ONYX, the gunboat HMS PYGMY and five other submarines. PYGMY and the submarines A7 and A9 took station off Rame Head and completed two attacks. As PYGMY started her next run, A7 dived. It was soon apparent that the attack had failed after A7 failed to surface. The wreck was not located for six days after which its location was indicated by an oil slick.
A7 was found upright at an angle of 35 degrees with her stern buried deep in the mud. Because of a heavy swell, no attempt was made to pull her from the mud until 28 January. A 5.5-inch hawser was secured to a forward end eye-plate, but the pull resulted in the fracture of the eye-plate. Further attempts were not made until 17 February, when a larger hawser slipped when trying to free her. Ten days later another attempt ended in failure and the operation was abandoned. The submarine is an official war grave.
There is an excellent 33 minute documentary about the loss of HMS A7 here.