4 May 1942
Madagascar, a mountainous large island in the Indian Ocean, consists of many rivers and high rainfalls. was previously a French colony controlled at the time by the French Vichy government. The British were afraid that the French, would allow Japan to set up military bases on the Island. If this happened, it would have seriously threatened its sea routes leading to India and Ceylon.
On 4 May 1942 British troops landed in the Bay and Bay Ambararata Mail, just west of the port of Diego Suarez at the northern tip of Madagascar. Britain then attacked its ally, France.
The British decided to capture Madagascar, and handed it over to the Free French to control in order to consolidate their own routes to the East safely
References
Clayton, C.J.A., The South African air force in the Madagascar Campaign, from SA Military History Society, [online], Available at samilitaryhistory.org [Accessed:16 April 2014]|Dessert War, World War II, from dessert war net, [online], Available at www.desertwar.net [Accessed: 16 April 2014]