Factual error: In the scene at the Bangkok docks, the ship has the name Athena but with the Greek letter Lambda instead of each capital letter A. This would make the name something like Lthenl, and is a nonsense mix of Greek and English (Roman) letters.
Factual error: Ka-Bar knives with serrations on the blade were not sold until the 1990s.
Factual error: When Packard and his men arrive on the island, they are seen wearing ALICE gear (All-purpose Lightweight Individual Carrying Equipment). The film takes place in 1973, that type of gear would've just finished testing phases in 1973. The soldiers would be more accurately equipped with M-1956 Load-Carrying Equipment (LCE) or M-1967 Modernized Load-Carrying Equipment (MCLE).
Factual error: When she is detailing her military experience Mason mentions she was "embedded with MACV-SOG." The practice of embedding journalists with military units during wartime did not become a formal practice until the Iraq War of 2003. Prior to that many journalists during the Vietnam War, like Joe Galloway who was with the 7th Cavalry at the Ia Drang Valley, had to find their own way to the battlefield. Additionally "embedding" was not a term that would have been used by the military or the press at that time.
Factual error: In the beginning Packard is in his office and opens a brown cigar box. That is a Rocky Patel box that wasn't developed in the cigar industry until 1995.
Factual error: All the helicopters shown have wire strike protection systems fitted. They weren't produced until 1979.
Answer: The chains are anchor chains from the ship wrecks that were there.