Poor visibility or inattention could cause collisions as catastrophic as an enemy attack when dozens of merchant ships and escorting warships assembled into convoys.

Donald Mackay depicts an officer aboard a corvette using a speaking trumpet to hail a looming merchant vessel. During the Second World War, several Canadian warships were damaged in collisions and four were sunk. The merchant ship Port Fairy cut the destroyer HMCS Margaree in two on 22 October 1940, with the loss of 138 sailors, including many who had survived HMCS Fraser's sinking through collision four months earlier.

Fog, Foc'sle of Corvette and Bow of Merchant Ship in Fog
Painted by Donald C. Mackay in 1943
Beaverbrook Collection of War Art
CWM 19710261-4221