This is an ac40 date added variation.  This was a P.38 that was originally manufactured as an ac no date and then, due to military directive, had the date of "40" added below the ac code.  This gun unfortunately must have been stored in a wet holster as the surface of the slide, especially on the right side is slightly etched which removed a lot of the blue in that area.  The big plus is that this gun has 2 original matching magazines.  Also interesting is that the left side of the mags were electric pencil etched with the serial number (no suffix) and the "+" indicating the spare magazine.  Why could never be determined but maybe the magazine fitter was caught at a time when he could not immediately forward the mags to the stamping machine and etched them so he would not lose track of what he had done.