On 28 June 1942 German troops in Russia started Operation ‘Blau’, the aim of which was to destroy the Bryansk front and to break through the South East front. By 12 July both had been breached and German troops advanced south-east, threatening Soviet communication lines with the east and the key oil supply route. Throughout the summer it appeared that nothing could stop the relentless German progress. On 23 July Rostov fell. At this point the German army divided in order to proceed in two different directions: one towards the Don where it got bogged down at Stalingrad and the other, Army Group A, south-east towards the oilfields of Batum. The latter move was particularly successful. By August it reached the coast of the Black Sea and looked likely to succeed in capturing the Baku oilfields and destroying the Russian North Caucasian front. By September German troops were moving south along the Black Sea coast towards the strategic bases of Temryuk and Novorossijsk. In the meantime Stalin himself had decided that a stand had to be made in Stalingrad. Key German units in the south were in due course diverted away from the successful drive to the south-east and into the stalemate which developed around Stalingrad.

In spite of this loss of momentum the allied strategists feared that the German progress to the south-east would have very serious diplomatic repercussions.