During World War II, Madagascar was actively involved in military operations, particularly the Allied invasion known as Operation Ironclad in 1942. This was aimed at taking control of the island to prevent it from potentially being used by Axis powers.
Robben Island was primarily used as a prison and not a site of active military operations during the war. Seychelles, while it was important for its strategic location, did not see significant military conflict compared to Madagascar.
So, the correct answer is Madagascar.