What do the following phrases have in common?

COMMANDING OFFICER
DEFENSIVE END
PUBLIC ADDRESS
NAUTICAL MILE
GAMBLERS ANONYMOUS
OPERATING ROOM
MIDDLE ENGLISH

HINTS:
#1: It has to do with geography.
#2: It has to do with US geography.
#3: It has to do with initial letters.

Answer:

The initial letters of the two words in each phrase form the postal code of a US state:

CO - Colorado
DE - Delaware
PA - Pennsylvania
NM - New Mexico
GA - Georgia
OR - Oregon
ME - Maine

Credit: LA Times Crossword
Sylvia Bursztyn and Barry Tunick
GOING NON-POSTAL