OB 318 was a North Atlantic convoy which ran during the Battle of the Atlantic in World War II. During Operation Primrose Royal Navy convoy escorts HMS Bulldog, Broadway and Aubrietia captured U-110 with an intact Enigma machine and a wealth of signals intelligence, which led to the Allied breakthrough into cracking the German naval Enigma code.

HMS Bulldog (H91) was a B-class destroyer built for the Royal Navy (RN) between 1929 and 1931. Initially assigned to the Mediterranean Fleet, she transferred to the Home Fleet in 1936. During the Spanish Civil War of 1936–1939, the ship spent considerable time in Spanish waters, enforcing the arms blockade imposed by Britain and France on both sides of the conflict. Bulldog saw service throughout World War II on convoy escort duty during the Battle of the Atlantic and in the Arctic. Her most notable actions were the capture of an Enigma machine and codebooks from the U-110 in 1941, sinking another German submarine in 1944 and taking the surrender of the German garrisons on the Channel Islands on 9 May 1945. Surplus after the war, she was broken up for scrap in 1946.