Very little is known about the HK P11. It is a special pistol that fires underwater. What is known is that it will fire five shots, but after the five shots are fired, a significant delay in reloading, even slower than a revolutionary war muzzleloader. You must send the upper unit back to the factory for reloading!
HKPRO recently acquired more detailed information about the P11. It was designed in the 1970s, and entered service in 1976. It has never been officially acknowledged by HK. It fires darts of 7.62 x 36 caliber either above or underwater. The effective range of the P11 is reported at 30 meters above water, with a report barely louder than an MP5SD. Underwater, the effective range is 10-15 meters.
The P11 is reportedly in service with German combat divers, the British SAS, and 100 units to U.S. Specops forces. It is also used by Dutch, Danish, Norwegian and Israeli combat divers.
You saw this rare detailed glimpse of the HK P11 first at HKPRO.