1942: Unlikely bedfellows in Persia
The completion of the "Iron Line" across Turkey-Persia-Afghanistan- China in mid 1941 was the culmination of the worst fear of the Entente powers, China and her German ally being able to link hands from across the world and work together closely. It is unclear at this point however, how much the Entente saw the Iron Line as a legitimate threat or how much of it was hyped up as propaganda to justify cooperation with an ideological enemy (the Soviet Union) and a hostile military invasion of an officially neutral country.
Even prior to that, with the continued frosting of German-Soviet relations, unofficial talks had already begun. It was always Stalin's intention to sweep into the Second Great War after the forces of the Entente and Axis had fought themselves to mutual exhaustion, however, with the defeats of the Entente in 1941, the war looked to be tilting towards the favour of Axis. Stalin's response was twofold. The first was to step up the number of 'border incidents' around the Polish-Soviet Border, not with the intention of provoking full scale conflict, but to force Axis Germany to keep large contingents of troops near the border. The second was to pursue a policy of "Self-interested Co-Belligerence" with the Entente. The Soviet policy would not be to seek an alliance, but find areas of common ground and cooperation with the Entente powers. Secret talks were initiated between London and Moscow about the 'inconvenience' of having China and Germany united through a rail network (these talks tactfully ignored the fact that the Soviet Union did nothing to prevent these networks from being constructed in the first place when they had the opportunity.) The talks were successful and a joint military offensive "Operation Countenance" was agreed to. Operation Countenance was a military invasion of Persia with forces between the Entente and the Soviet Union where they agreed to stage an invasion of Persia with the primary objective of cutting off the Iron Line but with the secondary objectives of plundering Persia.
Persia had been drifting towards the Axis powers, with the Shah unilaterally nationalizing the oil fields in late 1941. A contingent of German and Chinese military advisors were already present and training the Persian military. German engineers and advisors were also at hand to support the recently renationalized oil fields. A secret guarantee had also been provided to King Reza Shah Pahlavi that Chinese and German forces would provide assistance in the event that Persia's territorial sovereignty was 'violated by any power.'
Iranian warship Babr destroyed at port. A common scene in the early days of Operation Countenance. (1)
The above was purely academic to the people of Persia on the 21st of March 1942 as bombs fell on palace district and all over Tehran and as Soviet and Entente troops fell upon Persia as Persians celebrated Nowruz (the Persian New Year.) King Reza was killed, along with many innocent Persians. The small Persian navy was also destroyed at harbour and the air force was gutted by surprise bombings. The Persian army fought bravely but was overwhelmed by the superior forces that the Entente had amassed from the South and that the Soviets had amassed from the North. Initial Persian resistance was hampered by difficulties in the chain of command with the King dead and the crown prince Mohammed Reza Pahvali taking time to recover from his injuries and resume the throne.
Soviet troops crossing the border on 21 March 1942. The Soviet use of trucks and other motorized transport was key to the success of the invasion.
The invasion was widely regarded as a surprise. There was no declaration of war and no expectation that the invasion, which was predicted to happen, would come so suddenly. The Persian military was only partially mobilized, with many reservists on holiday due Norwuz being a national day of celebration. Although Germany had begun forming the nuclei of a expeditionary force with the 2nd Mountain Division being transferred to the Turkish-Persian border, preparations were only about halfway complete with the division at half strength at the time of the invasion. China's Western Army Group had also been stripped of a lot of troops and was thinly stretched across a broad front and was only able to send a division of second-rate NRA troops to try and assist. The Axis troops were also hindered by awkward rules of engagement. They were only authorized to fight Entente troops and not Soviet troops and were thus deployed to the South to fight Entente troops. The 100 or so aircraft deployed in support of the Axis efforts were also not allowed to shoot down Soviet planes that were bombing or attacking the troops there. Stalin showed no such restraint, he knew he had the upper hand and that the Axis did not want to escalate a shooting match at this point.
The outcome of the conflict should not be a surprise. Despite fanatical Persian resistance which continued well into the occupation, organized military resistance ceased by the end of May with the remnants of the Persian Royal Army and Axis expeditionary forces dissolving into the countryside and mountains to continue guerrilla resistance - led by the Crown Prince Mohammad Pahlavi who had elected to stay in the country rather than attempt to flee into exile. By the end of the organized resistance, it is estimated that about 1000 of 5,000 strong 2nd Mountain Division that Germany had sent remained in the country, along with 2,000 NRA troops. These troops were trapped and continued fighting with the Persian Resistance and were led by Chiang Wei-kuo, who had been deployed with the 2nd Division. They, along with the prince and his resistance army prayed for salvation. It would take a long time for their prayers to be answered.
(1)
https://en.wikipedia.org/wiki/Anglo-Soviet_invasion_of_Iran#/media/File:Iranian_Warship_Babr.jpg
(2)
https://upload.wikimedia.org/wikipe..._troops_are_crossing_the_border_with_Iran.jpg