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.
After playing a record of Chicago sounds for Mrs. Hoyt, Hank mentions the "Elevated" (its transit system). No one from Chicago, as Hank is, would call it that - it's simply the "L".