Victory at Sea, the World War II documentary.
The footage may be old, as it was made directly after the war, but (as stated above) it defined an era when humanity's future was far more uncertain. My grandfather, to avoid being drafted into an infantry unit, enlisted into the Navy at a young age, and served proudly and heroically in the South Pacific naval campaign in a gunnery unit.
This footage is the only glimpse of the absolute Hell-on-earth he witnessed and survived.
Imagine for a second being completely blacked out at sea with several other battleships, cruisers, and carriers; pitch black; radio silence; just waiting; listening for the Japanese "zeros"; waiting for the order to fire; all you can hear is the water, the wind, and you and your friends heavy breathing. I can't begin to describe the dread, the adrenaline, the anticipation, prior to an attack; and then the sky lighting up like a life/death fireworks show from the primitive (by our standards) tracer-bullet guns they used to gun down the enemy. The orders were simple: kill them or they crash into the ship and kill a BUNCH of you and your friends.
Completely epic heroism and service. Courage defined.