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 20 miles ( 32 km ) 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 .