Source: Superman's Pal, Jimmy Olsen #86-87 (1965)
This particular Silver Age classic starts with Jimmy getting into the back of an armored truck made of Vulnite, which should be impregnable. He can get all the cool pictures from inside, you know? At about the time he surely realizes it's dark in there, criminals with a bazooka attack the truck and prove Vulnite (patent pending) isn't that great after all.
Don't worry. It's the Silver Age and Superman tricks the villains with some silliness or other. It's not important. Get back to your exams, kids.