Proof of Life might well satisfy those more knowledgeable in real-life military matters. When Terry (Crowe) explains to Alice (Ryan) how he started out in the Australian Army, but left for the British Army because there wasn't enough action...he was stating a very plausible possibility. The British Army does indeed accept recruits from Commonwealth nations. Terry also says he is veteran of the elite British Special Air Service, and again, it is true that a huge proportion of ex-SAS members end up in private security efforts of various kinds. When the big raid is carried off, the costumers took enough care to dress Terry in British DPM fatigues, while the American Dino (Caruso) wears American BDU fatigues. Again, this is plausible as these are the sorts of fatigues both men took with them when they left military service. I've seen a lot of reviewers here criticize the end raid sequence.
I found the actions scenes very good and a welcome change from most movies. Terry and Dino actually plan for covering fire from higher ground, fields of fire, etc. So many military raids in movies (The Dogs of War is a good example) just have the characters march out in the open and fire from the hip, with no seeming plan of movement other than to run around, destroy stuff, and look dramatic. Terry and his team never stuck around any longer, nor killed any more of the guerrillas, then necessary to rescue the hostages and escape.
I can see where these details failed to find appreciation with the general viewing public, but I only hope others doing such movies continue to try to be authentic and realistic.
