Wather introduced its first pistol in 1908, creatively named the Model 1. With the outbreak of World War One, the company was offering the Model 4 pistol for military use. This was a .32 ACP simple blowback action, and it proved quite popular and successful. However, the German military was primarily interested in 9x19mm handguns for front line service.
In an attempt to serve that market as well, Walther developed the Model 6, a scaled-up version of the Model 4 chambered for 9x19. The Model 6 remained a simple blowback pistol, with a heavier slide and mainspring to accommodate the much greater muzzle energy of the 9x19 cartridge. It entered production in 1915, but only a little more than a thousand examples were manufactured by 1917, when production ceased. While the gun did work well enough, the 9x19 cartridge is not really well suited for a blowback system, and the military much preferred locked-breech siderarms. The Model 6 was not formally adopted, although many of the guns made were purchased privately and did see use in the war.
Othais' history of the Walther Model 4: https://www.full30.com/video/9f8c893731a4ee2303cfb497c7e859e2