The next assignment, Operation Ironclad, was the invasion of Madagascar, the third largest island in the world and then under Vichy French control. The Prime Minister and the Combined Chiefs of Staff decided that Madagascar should be occupied as rapidly as possible to deny the port of Antsirane to Japanese naval forces, which had recently advanced into the Indian Ocean. Operation Ironclad was under the command of Major General Robert G. Sturges and consisted of No. 5 Commando, 29th Independent Brigade Group, and the 17th and 13th brigade groups from 5th Infantry Division. The 29th Brigade formed the core of the invasion force due to its training in amphibious operations, and under its command was 'B' Special Service Squadron, created by amalgamating six Valentines from 'B' Squadron and six Tetrarchs from 'C' Squadron into a single unit. The squadron was formed into four troops, one Headquarters troop of three Valentines and one Tetrarch, one of four Valentines, and two formed from the remaining five Tetrarchs. The invasion force assembled off the west coast of the northern tip of Madagascar on 4 May, near Antsirane and the bay of Diego Suarez. The invasion plan called for an amphibious assault landing on four beaches on the west side of the tip, which would allow the British forces to advance approximately and approach Antsirane from the rear. Information about the landing beaches, the defences possessed by the port, and the Vichy French defending forces was limited and vague, although it was believed that the defenders had no weapons capable of penetrating the armour of a Valentine tank.