Thanks! I have a weird fascination for war movies. When you first posted the image, I thought the guy under the helmet supposedly misunderstood the order and fired. :-)
That's exactly what happens, just it's not the guy in the helmet that is on fire control.
The movie is about military attitudes and brinkmanship. Poitier plays a questioning reporter to whom the ready (at battle stations) procedure is being explained, by the Captain (Widmark).
I won't spoil it further for you, and you can find the critical scenes on You Tube, maybe the whole movie.