4. The First Time Superman Switches Costumes With Batman
World's Finest Comics #71
Lois Lane sees Clark Kent changing into his Superman outfit. A worried Superman confides the situation to his bestie Batman who comes up with a brilliant plan: swap their costumes.
The plan to confuse Lois involves Batman letting her see him change out of his Superman costume into his regular Bruce Wayne attire. Then he has her catch him doing Superman stuff: like having a pretend fight with trained lions so she will think he’s super strong. Which has all sorts of problems. Having people know Bruce Wayne is the human identity of a superhero is dangerous regardless of whether he is actually Batman or Superman.
What's the real Superman dressed as Batman been doing? He got himself knocked out by kryptonite and has been passed out for days. Lois finds him and pulls off his mask, recognizing Clark. She then assumes not that Clark is secretly Batman, but that he was pretending to be Batman in order to get some sort of scoop.
A revived Superman puts back on his own costume in secret and then drops Lois off at the Daily Planet just it time for them to see Bruce Wayne. Lois Lane, a brilliant journalist known for her investigative writing skills doesn’t make the logical leap that maybe Bruce and Clark are both superheroes. Thus, the story ends with both their secret identities staying super-secret.