During the "Frankfurt Special" number on the train, Tulsa's seating position changes twice.
In the opening scene when Elvis and another soldier are loading ammunition into the tank, the shells being loaded are much too large for the main tank gun, which was 90mm on the M48 tank.
Lili offers to make food with Liederkranz, a Limburger-like cheese, but Liederkranz cheese was never authentic German cheese; it was developed in the USA by the developer of Velveeta.
When Elvis is singing in the train, he keeps moving his left leg (knee), he stops playing the guitar to touch his left knee, but the guitar can be heard playing.
The scenes with the tanks in the beginning are partly and visibly sped up.
In the shower scene, all shown waist-up naked, besides a sergeant showering along with enlisted men, when focusing on him after Elvis takes his soap, the sergeant is shown putting his hands down towards his waist, in a sort of pulling up shorts gesture - despite, all being supposedly, presumably naked for proper showering ablutions.
While Elvis is stood around in his tank overall, his name reads as Maclean but when his name is written down (or even credited) it's Mclean.
When Tulsa brings the baby to Lili's apartment after breaking his bottle, childless Lili either just happens to have a baby bottle or finds one at 2:30 AM.
When the G.I.s are on the train to Frankfurt, Elvis is singing "Frankfurt Special." He stands from the seat playing an acoustic guitar, but the music heard is actually an electric guitar.
Interesting that nobody in Germany seemed to speak German.
The G.I.s are wearing underwear in the shower.
When leaving the Cafe Europa, Tulsa stands half a head taller than Lili. In actuality Elvis was only a half inch taller than Juliet Prowse's 5'11".
About five minutes from the end Lili says to Tulsa "you underestimate your attraction" but she should have said "you overestimate your attraction" as she was putting him down and not complimenting him.