List of Ace western numeric-series single titles  Ace Books have published hundreds of western titles, starting in 1952. Most of these were Ace Doubles (dos-à-dos format), but they also published a few single volumes. Between 1952 and 1968, the books had a letter-series identifier; after that date they were given five digit numeric serial numbers. There are 38 number-series western titles in the list below, but it may be incomplete. The list given here gives a date of publication; in all cases this refers to the date of publication by Ace, and not the date of original publication of the novels. For more information about the history of these titles, see Ace Books, which includes a discussion of the serial numbering conventions used and an explanation of the letter-code system.