At 08.46 hours on 21 Jun, 1940, HMS Prunella (X 02) (A/Cdr E.L. Woodhall, DSO, MVO, RN) was hit on the starboard side near the bridge by one of two torpedoes fired by U-28 in the Southwest Approaches. The explosion blew open the hatches of #1 hold, put the Asdic and steering gear out of order and mortally injured two crewmen. The panic party abandoned the now slowly circling ship in two lifeboats but the U-boat did not surface and fired a coup de grâce after about one hour that hit on port side amidships, causing her to slowly settle by the bow until sinking with a list to port at 12.30 hours.

The survivors found themselves in two lifeboats, one jolly boat, two Carley floats and a raft which they tried to keep together until losing touch the next morning in bad weather. Two days after the sinking, the 27 survivors in one of the lifeboats were picked up after being spotted by a Sunderland by the French steam merchant Casamance in 48°10N/08°28W and landed in Falmouth on 25 June. 13 survivors were picked up from a raft by HMS Versatile (D 32) (Cdr J.H. Jauncey, (retired), RN) in 48°47N/07°59W on 27 June and landed the next day in Devonport. The commander, seven officers and 48 ratings were lost.