https://en.wikipedia.org/wiki/P-38_can_opener

Cheap, indestructible, disposable, effective, safe, can double as a screwdriver in an emergency. Easy to figure out how to use, even by the FNGs. Every package of rations came with one.

The P-38 is easily used. First, the cutting point is pivoted to its 95-degree position,[5] from its stowed, folded position. Then, for a right-handed user, the P-38 is held in the right hand by the flat long section, with the cutting point pointing downward and away from the user, while also hooking the edge of the can through the circular notch located on the flat long section next to the cutting edge. The can is held in the left hand, and the right hand is rotated slightly clockwise, causing the can lid to be punctured.

The can is then rotated counter-clockwise in the left hand, while the right hand rotates alternatively slightly counter-clockwise and slightly clockwise, until the can has been rotated nearly 360 degrees and the lid is nearly free. The lid of the now opened can is lifted, most often with the P-38 cutting edge, and the P-38 is wiped clean, and the cutting point is rotated back to its stowed, folded position. The P-38 is then returned to its stored location, whether that is dangling on a dog tag chain around one’s neck, or in one’s pocket if the P-38 is attached to a key ring.

And only one moving part! A triumph of twentieth century military engineering design.