During WWII three companies made P-38 pistols, Walther, Mauser, and Spreewerk.
In order to conceal who made what, the Nazi's assigned codes to all arms manufacturers to be used instead of company names.
Walther used code "480" to around 1940 then switched to code "ac". (Note the small case letters).
Mauser used the code "byf" until early 1945, then switched to "SVW". (Note the change to large case).
Spreewerk used "cyq".
In order to identify a war time P-38 you need to take into consideration the maker, the year made, the serial number, and a "block code".
Usually the slides will be stamped with the makers code, a 4 digit serial number, the year made, and usually a block code of a letter.
Because of this system, it's possible to have a good many P-38 pistols all with the same serial number.
Here's how this was supposed to work.......
P-38 pistols were made in 10,000 gun blocks.
Starting at 12:00 midnight of a new year a serial number of 0001 was stamped on the first gun made after midnight.
These ran up to serial number 9999, then started over at 0001 again, only with a letter block code added of the letter "a".
Block code "a" serial numbers ran to 9999 a, then started over again at 0001 with a "b" block code, and ran up to 9999 b, and so on for the rest of the year.
So, in order to identify a P-38 you have to have the makers code, the year it was made, the serial number AND any block code.
Other wise you can have many guns with the same number and this could cause problems these days if a gun is listed as stolen but without ALL the identifying stamps.
In addition to those stamps, each maker was assigned an official military inspection office at the factories. Each office had a identifying code of numbers under the Nazi eagle.
Usually on P-38 pistols these were stamped on the right side of the slide, usually two or three times.
These office numbers are shown above.