Man's Best Friend Is Not His Dog - S4-E6
Revealing mistake: As Schultz holds Newkirk's hat during the search, you can see "Dawson" written on the inside band. This was to insure that Richard Dawson (Newkirk) always had the right wardrobe pieces.
The Return of Major Bonacelli - S4-E25
Revealing mistake: When Hogan, Carter and Le Beau are talking to Schultz, you can see it is an overcast day. After Hochstetter comes in and the camera cuts to them talking about Bonacelli, it goes back to Hogan. You can now see that they are on a sound stage. The reasons are that the guard isn't moving in The Tower, the boys are well lit, and as Hogan and Le Beau go into the barracks, you can see differences in the painting of the sky on the back drop.
The Witness - S4-E23
Revealing mistake: As Schultz comes in the barracks door, there is a sliver of the studio background visible by the door jamb above his head.
Clearance Sale at the Black Market - S4-E1
Revealing mistake: After Kiegel shoots out the bulb the light takes a couple of extra seconds to fade out.
Revealing mistake: While talking about Von Baler's daughter, Hogan is facing the building talking with Carter and Newkirk. Behind him is an open area of the camp. If you look, you can see that there is no guard in The Tower, no shadow of The Tower of the guard hut (the sun is behind them and Hogan), and the snow is piled up about three feet behind Hogan, suggesting that the background is a wall mural in the studio.
Clearance Sale at the Black Market - S4-E1
Revealing mistake: The Major goes to shoot out the light that the boys have turned on so Kinch can get the pictures. The first shot is angled too low to hit the bulb, but there is no impact on the front of the door's crosspiece; the smoke and dust comes from behind it. The second shot gets the bulb, but there is no muzzle flash, just sound. Also, there is no impact mark on the brick wall behind the bulb.
Color the Luftwaffe Red - S4-E8
Revealing mistake: When the truck with Hogan and company pulls up to the Luftwaffe HQ, the camera pans to the right to look at Klink getting out of the side car. When the camera cuts back to Hogan and company, they shake as if the truck just stopped, but it can be seen that the truck was stationary.
Revealing mistake: When Schultz is on the way out after giving the guys the news about the inspections and roll calls, you can plainly see that the background behind him is a matte painting. This is easy to spot because the building in the distance is lighter in color, and there are ripples in the fabric used.
Will the Blue Baron Strike Again? - S4-E12
Revealing mistake: When Hogan, Newkirk, and Carter are at the Blue Baron's secret airfield, Hogan opens the barrel and stuffs in a rag and lights it so it will be a flare for the Allied bombers. The flight line and the planes on it are an obvious cutout. The fire couldn't have spread to the surrounding ground like it was shown. Also, when the bombs were going off on the airfield, you can see that the explosions are very small charges behind the cut outs.
Answer: It's a solitary cell. Steve McQueen, star of 'The Great Escape' is known as the 'Cooler King'.