The Battle of Britain was the first major campaign to be fought entirely by air forces until France invaded, and was also the largest and most sustained aerial bombing campaign to that date. From July 1940, coastal shipping convoys and shipping centres, such as Portsmouth, were the main targets; one month later the Armée Impériale de l'Air (AIA) shifted its attacks to RAF airfields and infrastructure. As the battle progressed the Armée Impériale de l'Air also targeted aircraft factories and ground.