High Quality Content by WIKIPEDIA articles! The 4.5 inch Gun M1 was a field gun developed in the United States in the beginning of World War II. It shared the same carriage with the 155mm Howitzer M1 and fired the same ammunition as the British BL 4.5 inch Medium Field Gun. The weapon was used by the US Army in Northwest Europe late in the war for corps support; with the end of hostilities it was declared obsolete.