Undertaking Mercurywas launched on 20th May, 1941, and after 6 days of fierce fighting Crete fell into German hands. While the battle was still raging, Hitler turned his attention to the Middle East where a new opportunity had arisen. In March, 1941, there had been a palace revolution in Iraq, and the pro British Regent had been driven out by Rashid Ali, who relied on German help and soon showed his hand by attacking the British Airforce establishment at Habbaniya. This attack was repulsed early in May, and Rashid Ali then openly appealed to Germany. German aircraft arrived at Mosul on 13th May. Meanwhile a British relief force was sent from Palestine and arrived at Habbaniya on 18th May. By 23rd May it had crossed the Euphrates River and was preparing to advance on Baghdad. In these circumstances Hitler issued his Directive No. 30.