It was an attempt by Royal Navy Motor Torpedo Boats (MTBs) to stop the German auxiliary cruiser Stier from reaching Gironde, France.

[1] Stier made it through the English Channel and reached Gironde, but MTBs sunk the German fleet torpedo boats Iltis and Seeadler.

The German plan was for Stier, disguised as the minesweeper Sperrbrecher 171, to be escorted through the English Channel to Gironde, France.

[4] The German ships began picking up British MTBs on radar around two hours after midnight on 13 May.

[2] As Stier and its remaining escorts neared German shore batteries at Boulogne, the MTBs withdrew.