B-25H, "Wabash Cannonball", of the 491st Bomb Squadron in flight over China. Notice the 'smudge' behind the squadron emblem and below the pilot's side window. The smudge is the residue of the powder from when the side-mounted .50 caliber machine guns, are fired during a low-level attack on trains, rail yards, bridges, convoys, barges, troops, etc.
From the collection of Wozniak, combat photographer for the 491st Bomb Squadron, in the CBI.