The Sturmgewehr 45(M), also known as the MP 45(M) or the Gerät 06H (Halbverriegelt, German for "half-locked") is a German assault rifle.
The Gerät 06H was developed from the earlier Gerät 06 assault rifle, but with better mechanical ratios that allowed for the gas system to be omitted. When placed into service, the rifle was renamed the StG 45(M). The StG 45(M)'s intent was to replace the older StG 44, despite it only having been in service for one year. This was mainly due to the StG 45(M)'s lower cost of manufacture; the StG 45(M) cost 40 Reichsmarks to produce compared to the StG 44's 70.
Parts for only 30 rifles were manufactured by the war's end. However, the mechanism used in the weapon was later modified by Ludwig Vorgrimler for his rifle produced by CEAM, which was later developed into the CEAM Modèle 1950. The Modèle 1950 was later developed into the CETME rifle, but this system took off when Heckler & Koch started using it in a whole line of weapons they produced, including the famed G3 and MP5.
The Gerät 06H was almost identical to the Gerät 06, bar its half-locking roller-delayed blowback mechanism. Despite the lack of a gas piston compared to the older Gerät 06, the design required for the bolt to move while the bullet was still in the barrel and the spent case was fully pressurized; the use of traditional chambers caused case heads to separate during testing. The solution was the change from a traditional chamber to a fluted chamber, where longitudinal grooves were cut into the chamber, allowing gases released from combustion to float the case, assisting in extraction. This scorched the cartridges in a unique manner which was characteristic for later weapons made by Heckler & Koch using the same roller-delayed blowback principle.