Canadian aircraft discovered disguised Japanese submarine according to the U.S. Joint Intelligence Committee. Daily summary dated 14 April 1942

An item reported that a Canadian patrolling aircraft sighted on the position 54.03 North latitude and 132 West Longitude a small fishing boat fitted out with a pole mast. When the aircraft approached disappeared the boat without leaving traces. The pilot believed that he had seen a submarine. The J.I.C. commented that earlier reports confirmed that Japanese disguised their submarines as fishing boats.

Source

Map Room Papers (Roosevelt Administration), 1942 - 1945. U.S. Joint Intelligence Committee. Daily summary No. 125 dated 14 April 1942