This formal squadron portrait captures a U.S. Army Air Service unit at Mather Field, California, during World War I. Established in 1918 near Sacramento, Mather Field trained aviators and support personnel for the war effort. The men, dressed in wool service uniforms and campaign hats typical of the period, are arranged in the traditional four-row muster formation used for unit photographs. Two men in white mess attire, visible among the ranks, represent the squadron's attached kitchen staff. The photograph was produced by the Boosone Photo studio of San Francisco, a firm that documented many military units training in Northern California during the war. Project: 218714