During World War I, American soldiers commonly referred to incoming German artillery shells as "G.I. cans". Also during the war, "G.I." started being interpreted as "Government Issue" or "General Issue" for the general items of equipment of soldiers and airmen especially since back at that time. the air force was part of the Army in most countries, including the United States. The term "G.I." came into widespread use in the United States beginning with the start of selective service in the peacetime year of 1940 and extending into 1941, when the draft was much resented because the United States was at peace until the Attack on Pearl Harbor. Next, the use of "G.I." exploded during the war years of 1942 through 1945.