The HK P7 is one of the more unique types of HK pistols. The P7 was developed in the 1970s for the West German police, who were looking for a new 9mm pistol to replace the older .32 caliber Walther PPs and PPKs that they had been using. Three new 9mm pistols were adopted: the Walther P5, the SIG Sauer P225 (or P6), and the HK P7. Out of these three, the HK P7 is easily the most unique and innovative due to its neat firing system.
The P7 is a gas delayed blowback operated pistol. A modern pistol that utilizes a very similar system is the Walther CCP. A piston is contained inside of a cylinder located under the barrel of the P7. The gas pressures from a fired cartridge travels through a port in the barrel to cause the slide to travel rearward with the help of the piston.
The P7 is also referred to as the squeeze cocker due to the fact that the grip must be depressed in order for the weapon to fire a round. This is a good safety system that has not been replicated in other pistol designs.