'CK' (i) was a British naval undertaking to sink blockships in the Dunkirk channel (3 June 1940).

The undertaking was part of the programme to deny the Germans free use of captured French ports after the completion of the 'Dynamo' and other evacuations from the continent as France fell to the Germans in 'Gelb'. The destroyer Shikari, the motor torpedo boat MTB-107 and the motor anti-submarine boat MA/SB-10 departed the Downs with three blockships (1,975-ton Gourko, 1,791-ton Moyle and 687-ton Pacifico) to complete the Dunkirk channel blocking, but while on passage Gourko sank after colliding with a French personnel ship, or according to other sources after striking a mine, off Dunkirk. The motor torpedo boat and motor anti-submarine boat picked up seven and 10 members of the crew respectively.

The other two ships continued with 'CK' (i). Moyle rammed the inner western pier abreast of a wreck and scuttled herself, sliding toward the centre of the channel as she sank, and Pacifico's captain decided to use the position which had been allocated to Gourko, but the ship struck the wreck against which Moyle had first come to rest, swung broadside across the channel and was then scuttled.

Shikari then started to shell the German positions round Dunkirk and, after collecting some 383 men from the port’s eastern pier as she became the last ship to leave the French port as it fell to the Germans.