Sally,

Two things that I've noticed in looking over this:

1. The order that you evaluate things is important. Looking for "U.S." before "U.S.N." will always find the match on U.S., and not on U.S.N. You need to move the U.S.N. above the U.S.

2. You might want to change the prefix matching to not include the beginning wildcard - otherwise, names like "YACHT AUSTRALIA [III]" is finding a match on "US".