The HK P2A1 is a single-shot, break action flare pistol designed for signaling and illumination purposes.
It can fire either 25 mm or 26.5 mm flares, or smoke cartridges. Adapters are available to use commercial 12-gauge flares available at sporting goods stores.
The body of the pistol is mostly polymer composite, with the barrel and breech being made of steel. The P2A1 has a life expectancy of about 1500 shots of full power flares.
The P2A1 is called the "SigPi" in the Bundeswehr, standing for "Signalpistole" or signal handgun.