Walther Model 4 , Variation 5. The Model 4 was made from 1910 untill 1928. This was Walther's first truely successful pistol. It was purchased by the police and army and it was adopted as one of the sidearms for use by the post-WWI reichswehr. It also had very successful commercial sales. If you will post all markings and where they are located I might be able to give you even more information ( railroad, police issue, ). From the pictures I would say your pistol is worth 375 to 450.