Best book on Walther pistols?

What is/are the best book/s on Third Reich era Walther pistols? I managed to get a friend into WW2 collecting but he is gravitating toward handguns instead of rifles. Any suggestions?

Which Walther handguns is your friend interested in?

For the p38 series I would recommend The P38 Pistol, Germany’s famous service pistol in detail by Alexander Krutzek. Also, the Buxton three volume P38 series, though the books are older the information is still solid and it goes into more historical and development detail than the Krutzek book. Their is also a book dedicated to the spreewerke p38 but I’m not familiar enough with that book to know one way or the other.

I will have to leave anything about the other walther models pp, ppk, etc to other members.

I should have specified the PP/PPK earlier but did not. That being said I think he's shown some interest in P38s as well and will pass these along. Thank you.

In my opinion the best reference work on the IIIR PP/PPK series ....