Simple flare guns, common to all the armies engaged in Second World War, seemed to be ripe for modification. In German, two flare pistols immerged as capable both flash and bite, the Kampfpistole and Sturmpistole.
The Kampfpistol turned a standard flare gun of the period into a minature grenade launcher by rifling its short barrel. The rifling turned the smooth bore cartridges into something more accurate, via spin.
While capable of firing several non-lethal grenades, including as message grenade not unlike this one, the Kampfpistole's "Sprengpatrone." Often marked with a code Spr. Z, this grenade had a few ounces of explosive filler and could be launched out to 100 yards.
The small grenade prompted further development, leading to the Sturmpistole. A bigger grenade meant modifications were needed to the pistol. Instead of a standard break-open flare pistol, the Sturmpistole was turned into a complete system with a folding stock and sight.
With a smoothbore the Sturmpistole took a different route in development. A rifled insert was slipped onto the barrel. A sub-caliber, the insert would not allow the Sturmpistole to fire the larger diameter ammunition of the standard flare pistols.
The main ammunition of the Sturmpistole was the Panzerwurkorper 42LP. A High Explosive anti-tank round, the 42LP was best used at close range and at a 90 degree angle to the target. Under optimal conditions the grenade could penetrate 80mm of armor at about 50 meters.
This larger shaped-charge resulted in the pistol being tweaked. A sleeve and folding sight was mounted to the muzzle. And to increase accuracy an ingenious folding stock was attached to the pistol. Folding to the side, the stock turned the weapon into something much more compact. And the padded stock could then fold again, further reducing its silhouette.
Several hundred thousand Kampf and Sturmpistoles were produced during the war. And of its use on the battlefield, there is only one known recorded vehicle destruction by the Sturmpistole/ Panzerwurkorper 42LP.