There were two that immediately come to mind.

The first was an image of a completely nude ... and wet... sailor manning a machine gun in the blister of a PBY (The central gun emplacemant of a Patrol Bomber - Catalina) in the South Pacific, during the second world war. This photograph caused a furor - someone jumped to the conclusion that the sailor had shed his clothes because of the heat. The truth was something different.
The sailor had stripped to dive in and rescue a downed Airman after the PBY had landed off shore from an island - within range of Japanese machine guns, and lord knows what else. The Airman had been hauled on board, and the rescuing sailor had moved to his gun to return the Japanese fire without bothering to get dressed - while the aircraft began its takeoff run.

The second was considerably more grim. It was a photograph of a Russian Machine Gun nest during the Finnish-Soviet "Winter War" of 1939. The entire crew was in place - frozen to death, just about in the positions they would have held in combat. That bore stark testimony to the *harsh* Finnish weather and the total lack of intelligent preparedness on the part of the Russian Army - having sent their troops into battle during the worst winter in 50 years, clad only in summer uniforms.