The Walther PP ("Polizeipistole", or police pistol) series pistols were introduced in 1929 and are among the world's first successful double action, blowback-operated semi-automatic pistols, developed by the German arms manufacturer Carl Walther GmbH Sportwaffen. They feature exposed hammers, a traditional double-action trigger mechanism, and a fixed barrel that also acts as the guide rod for the recoil spring. It was offered in both .32 ACP (9-shot) and .380 ACP (8-shot) calibers. The Walther PP and smaller PPK models were both popular with European police and civilians for being reliable and concealable. They would remain the standard issue police pistol for much of Europe well into the 1970s and 80s. During World War II, they were issued to the German military, including the Luftwaffe.