Matilda I tanks equipped the 4th Battalion and 7th Battalion of the Royal Tank Regiment (RTR). In September 1939, upon the outbreak of the Second World War, the 4th RTR deployed to France with the British Expeditionary Force. They were joined at the start of May 1940 by 7th RTR and together formed the 1st Army Tank Brigade. Apart from light tanks assigned to the various British infantry divisions, this was the only British armoured force on the Continent at the start of the Battle of France on 10 May 1940. The 58 Matilda Is and 16 Matilda IIs spearheaded the counter-attack in the Battle of Arras on 21 May, temporarily discomfiting the 7th Panzer Division under Rommel. The heavy armour of both types of British tank proved to be resistant to the standard German 37 mm anti-tank gun and the attack was only halted by a gun line hastily formed from 105 mm howitzers and 88 mm anti-aircraft guns, personally directed by Rommel. On the following day, only 26 Matilda Is and two Matilda II tanks were still serviceable.