Developed from the pre-war "C-Class" Empire flying boats developed for and used commercially by Imperial Airways, the Shorts Sunderland entered service with the RAF in 1938. The robust design was progressively improved and increasingly heavily armed. Readily able to attack and defend itself on long range patrol missions, it earned the nickname the "Flying Porcupine" from its enemies because of these characteristics.

Sunderlands in Coastal Command participated in the destruction of 31 U-boats. Although no Sunderlands were officially on strength with the RCAF, in fact two RCAF squadrons, Nos. 422 and 423, were equipped with Sunderland Mk III aircraft. These Canadian-flown aircraft participated in the sinking of five U-boats and heavily damaged at least two others. In addition, another submarine was sunk after a Sunderland of No 423 Sqn homed two RCN destroyers onto the enemy vessel.