Although the title looks like a misspelling, Operation Greif was an actual covert operation conducted by Waffen-SS commando Otto Skorzeny and the brainchild of Adolph Hitler during the Battle of the Bulge in WWII.
Greif is German for griffon, a mythical animal with the head and wings of an eagle and the body and tail of a lion.
Most of the battle scenes in this episode were taken from the film To Hell and Back (1955) which was the true story of Audie Murphy, the most decorated soldier in United States history.
The opening scene would have us believe that all the infiltrators were near-perfect facsimiles of Americans. In reality, of the more than 200 Operation Greif applicants, only 10 spoke perfect English, the others were familiar with American idioms in varying degrees, while the majority spoke little or almost no English.