With the commencement of WWII, the US Navy took control of Wold-Chamberlain Field as Minneapolis-St. Paul International Airport was called. Flight operations by FBOs and commercial businesses were asked to leave, including those which had government contracts to train pilots. Only Northwest Airlines was allowed to maintain its terminal facility, while the Navy-Marine base at the north end of the field doubled in size, then doubled again as barracks, classrooms, an infirmary, mess hall, fire barn and even an olympic-sized pool were constructed.