As a theater commander in the Middle East, General Auchinleck was focused on the possibility of the Germans attacking from the north, either through Turkey or the Caucasus. He was no longer responsible for Iraq, as that had been given to the Commander in Chief in India. He and General Wavell had switched jobs, so Iraq now belonged to Wavell. A new concern was added when the ruler of Iran decided to become closer to Germany and Italy and get rid of British and Russian influences. In typical Churchill fashion, he insisted on calling Iran "Persia". That was a deliberate show of disrespect for the Iranian government. The British had helped to develop the oilfields in Iran, and felt that the country was a vital interest. General Quinan, in Iraq, was instructed to prepare to go into Iran.
He had limited resources in August 1941, when the order came. He had the 8th Indian Division, whose third brigade only arrived on 10 August. He also had the 9th Armoured Brigade, formerly Habforce. Despite the name, they were without tanks. It was joined with the 2nd Indian Armoured Brigade at Kirkuk and Khanaqin. The 10th Indian Division in northern Syria was added to General Quinan's available units. The 10th Indian Division was notable for having General Slim as division commander. They were up against a small Iranian army of ten divisions. They had about 524 artillery pieces and about 280 aircraft. The British and Russians were acting together and presented a joint ultimatum to the Iranian government on 13 August 1941. When the response was received, the invasion was planned for 25 August.
On 25 August, a brigade from the 8th Indian Division was landed at Abadan and took the island and refinery. Also on 25 August, another naval force landed troops at Bandar Shapur. The Iranian army surrendered by 28 August. This is based on the account in Vol.II of the Australian Official History.