This photo is a close up of the front left side of the frame and slide. The P.38 is the model. The 'ac' is the code for Carl Walther and the 43 is the year is was made, 1943. The frame has a "1", for the serial number and a Eagle over a "359", which is a Walther Military Acceptance Stamp.
To show you the same stamp wasn't used on each "1" please see photos 3, 5, 6, 10, 11 and 12. Notice each is different in appearance, depth and clearness. This proves that different stamps were used from different parts of the factory.