'Challenger' was a British unrealised plan within 'Backbone' for the seizure of Ceuta in Spanish Morocco in the event of a German invasion of the Iberian peninsula (1942).

Such an undertaking, if completed successfully, would have strengthened the British hold on the Strait of Gibraltar by providing a position to the south as well as to the north (Gibraltar) of the strait, and also served to reduce the strategic and operational significance of any British loss of Gibraltar to a German overland attack with or without Spanish support.