When I worked for the European Exchange System (PX system for military) in Germany after graduating from the Army in '70, I drove a beer truck for the EES & filled beer machines in the barracks (aka billets). All the cans I remember had NO pop tops. The cans were American beer, which I have no idea why anyone wanted anyway being in Germany. But, it was cheap. They were all punch cans. The beer can machine had a lever mechanism you'd set the can in & push & it would make both holes in the top. Again, this was early '70s.