Hitler was concerned that if Greece—which since 28 October 1940 was fighting against the Italians in Albania—became a British ally then the Ploesti oilfields in Romania, on which Germany relied for her fuel, might be open to air attack from Greece. As the Germans were planning an invasion of Russia for June 1941, they could not allow such a threat to their essential oil supplies, and so they began planning an invasion of Greece. In March 1941, Prime Minister Robert Menzies, of Australia, with the concurrence of his Cabinet, agreed to the sending of Australian troops to Greece to defend against a German attack. Both Menzies and the I Corps commander, Blamey, felt that the operation was risky and might end in disaster, but Menzies stated that Greece should be supported against German aggression and that the defence of Greece was a "great risk in a good cause".