The Division was formed in January 1941, out of the 20th, 21st and 25th Indian Infantry Brigades. Commanded by Major General William "Bill" Slim, it landed in Basra in April, moving up the Euphrates and capturing Baghdad and the oilfields of Mosul as part of the Anglo-Iraqi War. When Iraq's ally Nazi Germany relocated its aircraft to Vichy French Syria, the 10th invaded Syria from Iraq in June. The 21st Brigade advanced towards Aleppo, while the 20th and 25th Brigades guarded the communication lines and the Mosul oilfield, respectively. Following the French surrender on 11 July, the division returned to guard duty in Mosul. In August, the division took part in the joint Anglo-Soviet invasion of Iran. At the conclusion of the Iranian operation, it returned to Iraq, where it underwent additional training and undertook security duties until May 1942. In March 1942, command of the division passed from Slim to Major General Thomas "Pete" Rees when Slim was ordered to India to take command of Burma Corps, the kernel that would eventually become the British Fourteenth Army.