The Communist Chinese "gunboat" in the chase sequence was shown firing a Royal Navy pattern 6-pdr (Hotchkiss 57mm). However, close-ups of the gun crew showed what appeared to be a U.S. Navy pattern 3-in 23 caliber "boat gun" (same type used on the U.S. gunboat in the later "Sand Pebbles").
Whilst looking through the binoculars at the Chinese gunship, Hank is holding them upside down.