I got this from Wikipedia:
Stalag 13 was identified as located near the village of Hammelburg, and run by the Luftwaffe for captured Air Force personnel.
The show's premise was that the POWs were using the camp as a base of operations for allied espionage and sabotage against the German war effort and could leave and return at will. The prisoners operated a secret network of tunnels that led outside the camp, and had constant radio contact with Allied command. They were aided by the fact that the camp was overseen by the bumbling Colonel Klink and his aide Sergeant Schultz.
Hogan would routinely manipulate the simple-minded Klink and Sgt. Schultz into creating ideal situations for the secret operations conducted by the men at Stalag 13.
Possible inspiration for series
Many have also seen the interaction between the prisoners as being at least somewhat inspired by the 1953 feature film Stalag 17, a black comedy about a World War II German POW camp, released by Paramount Pictures, the same studio that currently owns the DVD rights to Hogan's Heroes. This movie even had a Sgt. Johann Sebastian Schultz, who appeared genial but was actually in league with the informant implanted among the prisoners. The producers of Stalag 17 later sued the producers of Hogan's Heroes for infringement.
Also, there was a real-life Stalag 13, and an Offlag 13 (which contained officers), located near a real German village of Hammelburg. The senior American prisoner there was Lt. Colonel Waters, son-in-law of General George S. Patton. In April 1945, Patton sent a task force on a raid to rescue the prisoners of Stalag 13. The task force got in, but all of the vehicles were destroyed getting out. Few of the soldiers managed to make it back to American lines. The Stalag was liberated about a month later. Books written about this effort include The Raid and 48 Hours to Hammelburg.
Also my friend Karl had this to say:
"...
noticed someone" custerman brig gen" telling that heidelberg had a
stalag, and if i had a picture. first of all the stalag in " ein käfig
voller Helden" a cage full of heroes was not located near heidelberg
but in lower franconia, stalag XIII D was in hammelburg north of
würzburg. hammelburg today is the infantry school of the bundeswehr
(federal army of germany) with special training for elite forces. the
stalag in hammelburg is known for the fail of the hammelburg raid which
was initiated by gen patton who had an accident near mannheim and died
before x-mas 1945 in the 130th station hospital in heidelberg...."
