In early June 1940, the Italian "Regia Aeronautica" attacked and besieged Malta, a British possession. From late summer to early autumn, Italy conquered British Somaliland and made an incursion into British-held Egypt. In October, Italy attacked Greece, but the attack was repulsed with heavy Italian casualties; the campaign ended within months with minor territorial changes. Germany started preparation for an invasion of the Balkans to assist Italy, to prevent the British from gaining a foothold there, which would be a potential threat for Romanian oil fields, and to strike against the British dominance of the Mediterranean.