When Gestapo Guenther takes Kronman away, Klink gives a 'Heil' and then starts to sit down without a chair underneath him. But when the camera angle changes, he sits right down in a chair.
Stock footage of an American cargo plane is used to show "Alfie the Artist" being parachuted close to Stalag 13. The plane is, in select spots, painted "International Orange." Tactical airplanes in wartime would not be painted as such.
Many times the wash basin plumbing in the barracks is used as a periscope and the piping is routed up and over the back splash. Here, the plumbing jets out from the wall making it impossible to lift it as a periscope. This is clearly seen when Col. Hogan goes to wash out his cup. (6:40)
Newkirk was an expert safe-cracker. Yet they needed to bring in someone else to blow this safe. What they eventually did, Newkirk could have done it.
The transport aircraft that delivers the "safecracker" to a drop point near Stalag 13 is a C-119. This aircraft did not exist during World War II. It was first manufactured in 1949.
As Alfie finishes going through his tools, he closes a bright yellow plastic drill-bit box, similar to that sold by Craftsman. Plastic boxes were not available during World War 2, nor was it likely that a British subject would own Craftsman tools, as they were not sold in the UK until 2001.
The "safecracker" parachutes from a transport plane with USAF designations. The USAF was not created until 9/18/1947.
Also Irving Berlin was Jewish so his songs would have been banned by the Nazis on that basis alone.
LeBeau, Carter and Newkirk sing Irving Berlin's song "This is the Army" as a diversion. The Germans would not tolerate or applaud an American song because American songs were banned and considered decadent by the Nazis.
What eventually happened to Alfie was not mentioned. Whether he got away, went back to England, back to jail, was caught, etc., was not stated.
On a couple of occasions, Carter, who is not married, is clearly wearing a wedding ring.