Segal is quite the operator in fact had he been captured alone as William Holden did in that other famous POW part he played in The Bridge of the River Kwai, Segal would probably have swapped identities with an officer and he'd have made it work for him better than Holden did in his role. As it is he's doing a pretty good job of surviving, he's a street smart American kid from the slums for who this is just another jail and that's something he knows about.
That doesn't sit well with King and country British officer Tom Courtenay who spends every minute trying to nail Segal on something, anything from collaboration to theft. Segal proves too cagey for him.
In fact one way or another everyone does whatever he has to do to survive, something that Courtenay never learns. Even camp prisoner commander John Mills recognizes reality.
The Japanese are rarely seen here, unlike in The Bridge on the River Kwai. Presumably these guys are so deep in the jungle they need very little guards. Living on subsistence diet, the mostly British prisoner population police themselves and not once is there an attempt at an escape.
James Clavell who wrote the epic Shogun and Taipan about the Orient was a prisoner of war and wrote King Rat in collaboration with director Bryan Forbes who got great performances out of his mostly British cast. Two I didn't mention are James Fox who becomes Segal's interpreter and mistakes his usefulness for friendship and Patrick O'Neal who plays Segal's go-fer sycophant.
King Rat got two Oscar nominations for Black and white cinematography and art&set design and lost both to Ship of Fools. It ranks up there with the two William Holden classics as among the best prisoner of war films done. Definitely catch this one when broadcast.