Operation Postmaster was a British special operation conducted on the Spanish island of Fernando Po, now known as Bioko, off West Africa in the Gulf of Guinea, during the Second World War. The mission was carried out by the Small Scale Raiding Force (SSRF) and the Special Operations Executive (SOE) in January 1942. Their objective was to board the Italian and German ships in the harbour and sail them to Lagos. The SSRF under the command of Major Gus March-Phillipps left Britain in August 1941 and sailed the Brixham trawler, Maid of Honour, to the Spanish colony.

Bioko is an island 32 km (20 mi) south of the coast of Cameroon, and 160 km (99 mi) northwest of the northernmost part of mainland Equatorial Guinea. Malabo, on the north coast of the island, is the capital city of Equatorial Guinea. Its population was 335,048 at the 2015 census and it covers an area of 2,017 km2 (779 sq mi). The island is part of the Cameroon line of volcanoes and is located off the Cameroon coast, in the Bight of Biafra portion of the Gulf of Guinea. Its geology is volcanic; its highest peak is Pico Basile at 3,012 m (9,882 ft).