Amongst the names called out in the roll call scene when Captain Long returns from Benucci's office is 'Verity'. Yorkshire and England cricketer Hedley Verity, who served as a captain in the Green Howards, was captured in Italy and died there while he was a POW. It's a sufficiently unusual surname to be more than coincidence.
The character played by Sir Richard Attenborough is nicknamed "Bunter", a nickname Attenborough had in real life, bestowed on him by screenwriter, his close friend (and future producing partner), Bryan Forbes.
The attempted escapee at the start of the movie is Captain Dicky Lester.
Michael Caine has a blink-and-you-miss-it appearance on stage with Dennis Price when the stage set is being position before the performance of "Hamlet". He also appears later with a pin-up picture asking a bunk mate if he thinks she'll fit in the tunnel.
This movie's setting is a P.O.W. camp in Northern Italy during the summer of 1943.