HMS TARPON (Lt Cdr H Caldwell) sailed from Portsmouth on 5 April 1940 in company with HMS SEVERN. She was due to transit to Rosyth with Convoy FN 39 but was detached to patrol off Norway as the German invasion of Norway was expected. TARPON sighted and attacked the German Q ship Schiff 40 on 10 April. Schiff 40 sighted torpedo tracks and established sonar contact on TARPON.

The German ship had to break off its attack for an hour or so whilst British Hudson aircraft circled overhead. Once the Hudsons had departed, Schiff 40 depth-charged the sonar contact that they had been holding throughout. Oil and air bubbles were seen to rise to the surface. Several more attacks were conducted, and more submarine detritus emerged including a cocoa tin and ‘HM Ships Only cigarette packet. There were no survivors.