USAF Serials

[tim_raper]

...and to add to the mix, in the good ole days they used to use 0-xxxxx on tail numbers to indicate 'Obsolete', or over 10 years old.

[POL]

O- (The letter), to be pedantic

[alnewhaven]

Referred to on Baughers site
http://www.joebaugher.com/usaf_serials/usafserials.html

In the 1950s, many airplanes left over from the World War II era were still in service, exceeding their expected service lives of less than 10 years. In order to avoid potential confusion with later aircraft given the same tail number, these older aircraft had the number zero and a dash added in front of the tail number to indicate that they were over 10 years old. It was hoped that this would avoid confusion caused by duplication of tail numbers between two aircraft built over ten years apart. However, this was not always done, and it was not always possible uniquely to identify an aircraft by a knowledge of its tail number. This practice was eventually discontinued when people started refering to the number 0 as being a letter O, standing for Obsolete. The requirement for the 0- prefix was officially dropped on April 24, 1972.