Well, that’s the whole humor of the thing — imagining Jimmy Stewart opposite his normal character.
It should be noted that Jimmy enlisted before Pearl Harbor, AFAIK, he was the only Hollywood actor to do so (many of them became actors after the war, or joined after PH). I saw an interview with someone who was in Stewart’s squadron during WWII and they said that Stewart never took the “easy” missions, even though the brass would have been happy to let him.
He landed at least one movie role because of his service in WWII. I don’t remember the name of the film, but it was a Western where he’s tracking a killer cross country, before finally killing him at the end (which is when you learn that he was Stewart’s brother). The studio didn’t want to use Stewart in the role, since they didn’t think that he’d be believable in the role (“Too nice.”). The director proceeded to describe Stewart’s military service during the war, concluding with words to the effect of, “If the guy can do all of that, then surely he can be believable in this role.”
I don’t know, but suspect, that his service also played a part in him starring in Strategic Air Command. Funnily enough, June Alliyson who played his wife in that film, was married to a Hollywood director, who was shooting The Conquerer with John “I feel this Tartar wuh-man is fer me, and my blood says, 'TAKE HER!” Wayne at the time.
I’m missing something — what’s the funny part?
Have you ever seen The Conquerer?
It just seems irrelevant to Strategic Air Command.
Well, there’s the Powell/Allyson connection and while SAC seems dated, it is nowhere near as jaw droppingly bad as The Conquerer is.
Are you restricting yourself to American actors here? LTC David Niven comes to mind.
Yeah, I’m restricting it to us Yanks. WWII began before Pearl Harbor, so for a Canuck or Yurpeen actor to enlist before PH isn’t such a big deal, unless, of course, they did it before a certain paperhanging sonuvabitch decided to annex Poland. Not to besmirch the service of any who served during that war, mind you, but before PH, most of America was focused on staying out of WWII.
My dad got to meet and shake Jimmy Stewarts hand once during some AirForce function in the early 50’s.
I remember hearing Jane Fonda relate a story of how one Christmas when she was very little, she heard someone on the roof on Christmas Eve. Very excited to she rushed to the window to see ‘uncle’ Jimmy, dressed as Santa, and a little drunk, on her roof with a big bag of toys.
You owe me a new keyboard!
I think you kinda answered your own question there, he did it because it was funny, and it was funny because it was so out of character (both of JS and the character he was playing).
And I spit water all over my monitor. Damn it… 
He wrote that one on a piece of toilet paper, after waking up in a puddle of his own sick.
I’m so going to hell for laughing at this.
Save me a spot willya?
This is my new personal motto.
Could someone explain the joke?
Astorian said: others would have shrugged and said “I tired,”
I made a joke over that sounding like a lolcat caption.
Cervaise swung at my hanging curveball and knocked it into the cheap seats. 
To belabour:
Lolcats, if you haven’t seen them, are pictures of (generally) cats with (generally) pithy or ironic captions using the sort of poor spelling and grammar you might expect from a cat who has only marginally learned English. They tend to be evocative rather than grammatically correct. One of the common captions has to do with an in-joke from Something Awful, I think, for which the punchline is “im in ur base killin ur guyz” (or, in other words, “I’m in your base killing your guys.”)
So:
“Im n ur kokpit, bommin ur krowtz.”
“I’m in your cockpit, bombing your Krauts.”
Implying that the cat was a fighter pilot bombing, ah, German soldiers. Yes, kraut is a mean and naughty word and despite that rather commonly used in WW2 to refer in a derogatory manner to Germans. I suppose it would have been a little less offensive to make this “Im in ur kokpit, bommin ur nossies”, but A) I think some of the impact of the joke is added with the use of the archaic slur, B) I can only mildly imagine Jimmy Stewart calling someone a Kraut, C) It would have made me laugh even harder because of a hard to explain inside joke.
There. I’ve successfully made that joke not funny at all.
Complete highjack. I haven’t been to the Arclight since I visited my friend in LA years ago and we saw, “Master and Commander: The far side of the world.”. Does that incredibly hot redhead cashier still work there? To this day, meeting her was my favorite memory of that trip.
Oh, anyway, yes…Jimmy Stewart is awesome.