Unusually, he shows German military personnel, instead of his usual US Army subjects.
The image was taken from a story in DC Comics' Our Fighting Forces showing a German U-boat captain getting ready to torpedo an Allied vessel. As usual, Lichtenstein used the comic as a 'found object' but made a series of changes to the image which simplify and intensify the effect, and also create more formal patterning.
For instance, from the quite wordy original (in which the sailor in the background also speaks), he has distilled the action down to just two words, the title of the painting. The original Captain says "Ready all forward torpedo tubes!" - Lichtenstein's simply says "Fire torpedoes!"
Lichtenstein changed the composition by making the captain's face larger, to nearly fill the painting, and using the periscope to form a frame. There's more patterning on the periscope, all in stark black and white, with contrasts between cross-hatching on the grips, pinstripes on the shaft, and sinuous wiggles of wiring. Lichtenstein also introduced similar patterns to the wall at the back, suggesting almost space age technology and avoiding any blank space in the painting.
For Lichtenstein, 'action comics' were never quite active enough, so he also painted the Captain with his mouth wide open, as if he's yelling rather than simply speaking. This heightens the sense of urgent and extreme action.
It's surprising to find an oil painting that instead of pursuing the potential of the medium for shading and varying its tones chooses instead to use areas of flat colour; even more surprising to find 'high art' copying popular pulp comics. Lichtenstein contrasts the high emotion of the episode shown with the highly formal nature of its portrayal - something that intrigued him about comics, and that he exaggerates here withdraughtsmanship that seems to owe more to technical drawing than it does to the Old Masters.