Walther P.38 made in 1943.  This variation is the last of the Walther made "stack codes".  What makes this example somewhat unique is that the "43" on the slide is smaller than on the "ac".   The "P.38" along with the ac43 is positioned nearer the front edge of the slide than you typically see on stack codes and the "ac43" is closer to the "P.38" than normal.  I assume they were having problems with their stamping maching.  The smaller "43" examples start in the 5000L serial number range and run to the very early "m" block.  From that point on, the slide code is in a straight line and positioned much further to the right side of the slide.  This example also has the slightly "plum" colored frame that shows up occasionally on Walthers.