The two MPs who appear early on the film are named Mangold and Pennycate. This is an homage to Tom Mangold and John Pennycate, authors of the book THE TUNNELS OF CU CHI, which was an instrumental reference source for the screenplay.
All the signs in the so-called "Ho Chi Minh" city are in Thai, which doesn't look even remotely like Vietnamese. Vietnamese language is written in the Western alphabet, with accent symbols over some letters. Thai has its own alphabet, quite indecipherable to Westerners.
In real life, actor John Doman (who plays Paul Finnegan, Beckett's comrade turned adversary) was a lieutenant in the United States Marine Corps and Vietnam veteran, and served under the 3rd Marine Division.
M50 Sniper Rifle Remington 700 Rifle In the Vietnam flashback, a young Thomas Beckett is seen using a Remington Model 700 sniper rifle. Vietnamese police detective Quan (Byron Mann) later gives Beckett another Remington to use. When Quan asks what Beckett thinks of the rifle, he says that it is "the best damn sniper rifle ever made".