Unnamed cast members in cast listing

It's odd that for a Best Picture winner in 1957 so many speaking roles don't even get a credited/uncredited mention in the cast listing. There's Weaver (Shears' friend on burial detail and sick bay) and Jennings (the young British officer with the arm wound), who both try to escape with Shears, and then later Chapman, the Force 316 officer working with Warden, Shears, Joyce and Co.

None of these guys get any cast listing. Anyone know who the actors were? It's not a big deal, just found it kinda odd.

"Congratulations, Major. It appears that at last you have found yourself a real war." Ben Tyreen