the attacking force were left behind, unsupported by armour and overrun. Rommel retained the initiative, maintaining his strength in the cauldron while the number of operational British tanks diminished. A number of probes were sent to test the various opposing strong points and from 6 to 8 June, further attacks were launched on Bir Hakeim and repulsed by the French garrison. The 7th Motor Brigade and 29th Indian Infantry Brigade continued to harass the Axis lines of communications. Black Saturday, 13 June On 11 June, Rommel pushed the 15th Panzer Division and 90th Light Division toward El Adem and by 12 June had begun forcing the 201st Guards Brigade out of the Knightsbridge Box to Tobruk. The 29th Indian Infantry Brigade repulsed an attack on the El Adem box on 12 June but the 2nd and 4th Armoured Brigades on their left were pushed back by the 15th Panzer Division and had to leave their damaged tanks on the battlefield. On 13 June, the 21st Panzer Division advanced from the west and engaged the 22nd Armoured Brigade. The demonstrated a superiority in tactics, combining tanks with anti-tank guns in the attack; Rommel acted rapidly on intelligence obtained from Allied radio traffic intercepts. By the end of the day, the British tank strength had been reduced from to about the had established armour superiority and a dominating line of positions, making XIII Corps on the Gazala line vulnerable to being cut off. By the end of 13 June, the Knightsbridge box was virtually surrounded and it was abandoned by the Guards Brigade later that night, with their commanding officer Thomas Bevan having been killed the previous day. Due to these defeats, 13 June became known as "Black Saturday" to the Eighth Army. Rigel Ridge On 13 June, the 21st Panzer Division attacked Rigel Ridge in the middle of a sandstorm. The Germans overran part of the 2nd Scots Guards at the Knightsbridge Box at the west end of Rigel Ridge, overlooked by the 6th South African Anti-tank battery of the 2nd Field Regiment, Natal Field Artillery and a battery of the 11th Regiment RHA nearby. The South African gunners kept firing until their guns were destroyed, allowing the withdrawal of other Allied formations. The South African battery commander had decided to stay and maintain fire against the German tanks, to delay the Germans for as long as possible. The remaining guns