In late March 1941, soon after the arrival of German forces (the Afrika Korps) in Tripoli, Libya, to reinforce the Italians, their commander (General Erwin Rommel)—although ordered to remain on the defensive—quickly captured the British front line position at El Agheila. He then went on an offensive which, by mid-April, had reached as far as Sallum, Egypt. The sole remaining Allied position in Libya was the heavily fortified port of Tobruk, which Rommel had surrounded and placed under siege. The Allied response was restricted primarily to harassment by the Royal Air Force.