This is all pretty implausible, but its fairly entertainingly done. Sinatra does well with a surprisingly unsympathetic character, and his tetchy relationship with Howard provides much of the enjoyment of the film. Howard's role is relatively stereotyped, but he's a good enough actor to know this and still make his character believable. Director Mark Robson and his screenwriter Wendell Mayes have an understanding of British army attitudes that's obviously influenced by too many viewings of Bridge on the River Kwai. While Howard is a military martinet and a man of principle, it's Sinatra's practicality and collaboration with the enemy which initially brings the men dividends.
However, Mayes and Robson have ensured that it's not quite as simple as all that and Sinatra is faced with some of the dilemmas of war which were explored a couple of years earlier in The Guns of Navarone, e.g. is it better to shoot an unarmed man or woman and save lives, or let them go and risk the lives of many more? Here though, screenwriter Mayes doesn't offer the easy solutions which undercut The Guns of Navarone. Sinatra's decision to let an Italian officer go free results in the death of some of his own men. Later on he's faced with the choice of shooting an unarmed woman in the back or risk compromising his escape plan.
Unlike some of its contemporaries, Von Ryan's Express isn't afraid to kill off some of its major characters, and this at least stops things from getting too predictable. Although the supporting cast includes Wolfgang Preiss, John Leyton, Michael Goodliffe and Adolfo Celi, only Edward Mulhare, as the British padre who has to impersonate a German officer, gets a chance to really shine.
Like a lot of war films of its era, some of the action scenes aren't all that realistic. When the heroes ambush a platoon of German soldiers in a tunnel, the Germans all collapse decorously to the ground as if they've just fainted. No mangled limbs or hideous death throes. It's one of those films where you suspect the Germans will get up and brush themselves off as soon as the camera stops rolling.
Like The Train though, Von Ryan's Express benefits from using real trains (this time on the Italian railways) and a minimum of model work. This allows it to stand up pretty well for modern audiences. Many of the hazards faced by Sinatra and the others will be fairly familiar to anyone who's seen The Train or Northwest Frontier, but they're all produced with enthusiasm, and handled with some skill, and screenwriter Mayes ensures that there are still a few surprises in store.