The Army chooses a loose cannon, Maj. John Reisman (Lee Marvin) to train and command a squad of brig-rats on a suicide mission behind enemy lines before D-Day. The inmates are a motley crew of renegades, degenerates and non-com's (as in non-conformists), who need no training to be bad to the enemy. If they survive, their jail sentences (and for some, death sentences) will be commuted. If they don't, well, war is Hell. But it's not a cell. And these guys have nothing left to lose, given the situation, American kamikaze's, who might just make it to freedom, like any other soldier...if they make it through.
The movie is top-heavy with male character actors. Besides Marvin, there's Robert Ryan, Ernest Borgnine, George Kennedy, Robert Webber, Richard Jaeckel, and Aldrich's Mike Hammer, Ralph Meeker. Those are the good guys. The cons include Charles Bronson, Clint Walker, Telly Savalas, Jim Brown, John Cassavettes, Donald Sutherland, and Trini Lopez (hey, where's Don Rickles and Bobby Darren?)
Bronson gets a promotion in this one, becoming the Steve McQueen to Marvin's Yul Brynner, Cassavettes has the biggest character arc and the showiest performance (despite underplaying his death scene) winning a Best Supporting Actor nomination, Savalas has the most colorful role as a Bible-spouting psycho, and Jim Brown has the moment everybody remembers-sprinting across a courtyard throwing grenades down air vents, moving so fast the camera crew can barely keep him in the view-finder.
Aldrich—never one to be very conventional no matter what genre he was tackling—manages to make his anti-war, anti-authority statements in the story set-up—these guys have little choice but to hang it all out in combat, and, ironically, they're the best-suited to do all the dirty work, even if nobody is shooting at them in the initial stages. At the time of its release, the film got all sorts of flack for its violence, which Aldrich manages to get away with by merely suggesting things with quick cut-aways, but it looks extraordinarily tame today (and, in fact, would look tame two years later when The Wild Bunch would take movie violence to a whole new level). It might even get by with a light PG rating today.
But despite the dirt-dog-grubbiness of the whole thing, the director still manages to throw in some testosterone-laced sentimentality into it, then pulls back during the big action sequence as more and more men fall in battle and the director only affords them quick shots in death. Pretty soon, you lose track of who made it and who didn't, and a pre-End-Credits roll-call of the dead is the only verification—not everybody gets their death scene, further undercutting any sense of heroics, despite the war-time setting. And let's face it, most of the deaths occur by trapping the victims (party-guests mostly) in a cellar and burning them alive by drenching them in gasoline, and setting them alight with grenades. It's never made clear why this might help the Normandy Invasion effort, but one shouldn't look too closely at the movie for authenticity.