After the Japanese attack on Pearl Harbor in December 1941 the US was suddenly in desperate need of thousands of modern automatic weapons.

In comparison to its main rival, the famous Thompson, it possessed similar firepower, better accuracy, excellent balance, a lighter weight, a much lower cost, and greater ease of manufacture.

The Reising's bolt is much lighter due to its delayed blowback mechanism being the main determinant of the automatic rate of fire; and consequently the whole gun could be correspondingly light without detracting from accuracy and controllability.

The M50 Reising's delayed blowback operation, often classified as hesitation lock,[6] works as follows: as the cartridge is chambered, the rear end of the bolt is pushed up into a recess, in a manner similar to tilting-bolt locked breech guns; but whereas such weapons rely on an additional mechanism to unlock them, in the case of the Reising the end of the bolt that pushes against the back wall of this recess, is subtly rounded, while the wall is correspondingly curved.

From here the bolt can move to the rear removing the cartridge from the chamber; but the combination of mechanical disadvantage and friction the force of the gases must overcome to push the end of the bolt down has achieved a delay of a fraction of a second, allowing pressure in the barrel to drop to a level sufficiently low for safe and efficient cartridge extraction.

[7] There were four versions of the Reising, two selective fire models: the M50 and M55, and two semi-automatic only variants: the M60, a .45 ACP carbine,[8] and the M65, chambered for the .22 Long Rifle rimfire cartridge designed for training purposes.

While sharing many parts with the submachine gun the light rifle uses a gas piston, it was built in semi-automatic and fully automatic versions and issued with a 12 round magazine.

[12][13] [14] The Reising entered military service primarily because of uncertainty of supply of sufficient quantities of the Thompson submachine gun.

Most submachine guns fire from the open bolt position, meaning the full mass of the bolt slams forward when the trigger is pulled; with the closed-bolt system employed by the Reising there is much less movement involving far lighter components, and the resulting improved control in the moment before shooting gives better accuracy, both for semi-automatic and at the onset of full automatic fire.

Although the Thompson submachine gun was available, this weapon frequently proved too heavy and bulky for jungle patrols, and initially it, too, was in short supply.

[16] During World War II, the Reising first saw action on August 7, 1942, exactly eight months to the day after Pearl Harbor, when 11,000 men from the 1st Marine Division stormed the beaches of Guadalcanal, in the Solomon Islands.

The same date of Guadalcanal's invasion, the Model 50 and 55 saw action with the 1st Marine Raiders on the small outlying islands of Tulagi and Tanambogo to the north.

Tests at Aberdeen Proving Ground and at Fort Benning, Georgia, had found difficulties in blindfold reassembly of the Reising, indicating the design was complicated and difficult to maintain.

After the war, thousands of Reising Model 50 submachine guns were acquired by state, county, and local U.S. law enforcement agencies.

[4] H&R was justifiably proud of the Reising's superior accuracy and balance, lighter weight, and ease of manufacturing when compared to the Thompson.

However, the Reising's close tolerances and delicate magazine proved unreliable in the sand and mud of the Solomons, unless kept scrupulously clean.

The gun quickly became despised by front-line Marines, and Lieutenant Colonel Merritt A. Edson, Commander, 1st Marine Raider Battalion, ordered that his troops' Reisings be flung into Guadalcanal's crocodile-infested Lunga River, as his troops resorted to reliable bolt-action M1903 Springfield rifles.

The retaining pins had to be delicately tapped out whenever the bolt needed to be removed for cleaning; again, an awkwardly involved task whilst under fire.

Lastly, the commercial model commonly has a smooth take-down screw, a two-hole trigger guard, and serial numbers ranging from one to 20,000.

They routinely have 14 fins on the barrel, a two-piece magazine release, outward flanges on the safety/selector switch, sling swivels, stock ties (crossbolts through the forearm), and a knurled take-down screw.

Finally, the military model commonly has a three-hole trigger guard, proofmarks like "PH" or "Pm2" above the chamber, and serial numbers ranging from 20,000 to 120,000.

H&R sold their remaining inventory of submachine guns to police and correctional agencies across America who were interested in the Reising's selective-fire capability, semi-auto accuracy, and low cost relative to a Thompson.

Then, faced with continued demand, H&R resumed production of the Model 50 in 1950 which sputtered to a halt in 1957 with nearly 5,500 additional submachine guns manufactured.

[4] Decades later, in 1986, H&R closed their doors and Numrich Arms (aka Gun Parts Corporation) purchased their entire inventory.

These weapons all have an "S" preceding the serial number and were sold domestically in the early 1990s after reparkerization and fitting with newly manufactured walnut stocks.

[4] In New Zealand in December 1963, two men thought to have been operating an illegal beerhouse business were murdered execution-style with a Reising submachine gun.