'Pentagon' was the Free French occupation of French Somaliland on the northern side of the Horn of Africa (26/28 December 1942).
Commanding the strait between the Gulf of Aden and the Red Sea, French Somaliland was originally part of Somalia which had been divided between France, Italy and the UK at the end of the 19th century. After the fall of France in June 1940, the governor, Hubert Jules Deschamps (followed on 25 July 1940 by Gaetan Louis Elie Germain and from 7 August of the same year by Pierre Marie Elie Louis Nouailhetas) sided with the Vichy French régime, but the officer commanding the colony’s forces, Général de Brigade Paul Louis Victor Marie Legentilhomme, left with his troops to fight alongside the British against the Italians in the East African campaign.
There were also a few defections from French Somaliland during 1941, when some air force pilots escaped to Aden to join the Escadrille française d’Aden, and Capitaine Edmond Magendie began training a number of non-commissioned officers who would become the backbone of the Bataillon de Tirailleurs Somalis, which later fought in Europe. Some Free French sloops also took part in the naval blockade which the British initiated.
Lieutenant General Sir William Platt, the British commander-in-chief in East Africa, codenamed the negotiations for the surrender of French Somaliland as 'Pentagon' because there were five sides: himself, the Vichy French governor, the Free French, the British ambassador in Addis Ababa, and the USA.
Only after 'Streamline' and 'Jane', which secured the British conquest of Madagascar between September and November 1942, and 'Torch', which saw the landing of Allied forces in French Morocco and Algeria in November 1942, did one-third of the Somali garrison, the 1/Tirailleurs Sénégalais under the command Colonel Sylvain Eugène Raynal, cross the border into British Somaliland and defect. This prompted the new governor, Christian Raimond Dupont, to offer the British an economic agreement without surrender, but this was rejected and Dupont was told that only if the colony surrendered without hostilities would the French right to the colony be respected in the post-war order. Dupont then surrendered and Raynal’s troops crossed back into French Somaliland on 26 December 1942, completing its liberation by 22.00 on 28 December with the unneeded support of a British naval force, from Aden, comprising the light cruiser Ceres, the destroyers Hero and Free Greek Panther, and the minesweepers Poole and Romney.
French Somaliland then became an element of the Free French faction led by Général de Brigade Charles André Joseph Marie de Gaulle.