'Longhop' was the Allied overall designation used by General Douglas MacArthur’s South-West Pacific Area command for the development of operations against Manus island, the largest of the Admiralty islands group on the northern side of the Bismarck Sea off northern New Guinea (1943).

In July 1943, following his decision not to attempt to take Rabaul on New Britain island, MacArthur was encouraged by the Joint Chiefs-of-Staff, who had discussed the strategy of the South-West Pacific Area at the Quadrant conference of May 1944 in Quebec, instead to take the Admiralty islands group. This was well sited in strategic terms to seal the ring round New Britain and New Ireland, possessed a superb protected anchorage at Seeadler Harbour, and had ample level terrain for airfields on Los Negros island to the east of the harbour. By taking the Admiralty islands group, moreover, MacArthur’s forces would bypass the large Japanese force at Hansa Bay on the north coast of New Guinea.

A target date of 1 January 1944 was set for what developed as 'Brewer', but this was pushed back to 1 April by the 'Backhander' landing on Cape Gloucester and a dispute over the appropriate command arrangements resulting from the fact that Admiral William F. Halsey’s South Pacific Area controlled the 'Seabee' construction units needed to build the naval base. The decision to make Halsey responsible for developing the base was not made until 28 February 1944.