A Martin B-10 bomber and its ground crew photographed at an airfield in the Panama Canal Zone during the 1930s. The B-10 was the U.S. Army Air Corps' first all-metal monoplane bomber and a landmark in aircraft design, combining retractable landing gear, an enclosed cockpit, and a rotating gun turret. Aircraft like this defended the strategically vital Panama Canal in the years before World War II. Project: 218476