When were ZIP codes first introduced?

Question

Were those numbers always called ZIP codes?

Answer 1

The postal service implemented postal zones for large cities in 1943.


By the early 1960s a more general system was needed, and on July 1, 1963, non-mandatory ZIP codes were announced for the whole country. Robert Moon, an employee of the post office, is considered the father of the ZIP code. He submitted his proposal in 1944 while working as a postal inspector.

The post office only gives credit to Moon for the first three digits of the ZIP code, which describe the region of the country. In most cases, the last two digits coincide with the older postal zone number


In 1967, these were made mandatory for second- and third-class bulk mailers, and the system was soon adopted generally. The United States Post Office used a cartoon character, Mr. ZIP, to promote use of the ZIP code. He was often depicted with a legend such as "USE ZIP CODES" in the selvage of panes of stamps or on labels contained in, or the covers of, booklet panes of stamps. Curiously, the only time the Postal Service issued a stamp promoting the ZIP code, in 1974, Mr. ZIP was not depicted.


ZIP+4
In 1983, the U.S. Postal Service began using an expanded ZIP-code system called "ZIP+4", often called "plus-four codes" or "add-on codes."

A ZIP code is the postal code used by the United States Postal Service (USPS), which always writes ZIP with capital letters. ZIP is an acronym for the Zone Improvement Plan but was also meant to suggest that mail travels more efficiently (and therefore faster) when senders use it. The basic format consists of five numerical digits. An extended ZIP+4 code includes the five digits of the ZIP code, a hyphen and then four more digits, which allow a piece of mail to be directed to a more precise location than by the ZIP code alone. ZIP Code was originally registered as a trademark by the U.S. Postal Service but its registration has since expired.

Answer 2

Ok, I'm really guessing here, but I think it was about 1959. Before that, the mail service used Zones. The zone represented a portion of the state, I think, and then when zipcodes came along, the former zone was the last number in the zip.
I just looked it up, 1963 was voluntary use of zipcodes but were suggested in 1943.