The Birth of the MP40

The most significant initiative to boost production came under the pressure of Dr. Ing. Anton Peter from the Amtsgruppe Entwicklung und Prüfung des Waffenamts – Infanterieabteilung WaPrüf2, also known as “Stahlblech Peter” (Sheet Metal Peter). The aim was to stop using the scarce manufacturing resources of the factories to produce the labor-intensive, milled bolt housing, magazine housing, and frame. The aluminum pistol grip also had to be replaced, as aluminum was a Spahrstoff. Only the milled parts, such as the barrel, the bolt, the locking nut, and a few small components that couldn’t be made otherwise, were exempt from being replaced with sheet metal.

Manufacturers with extensive experience in Blechprägetechnik (sheet metal processing) and the capacity to meet high demand were sought. Two companies, known primarily for producing typewriters in the 1930s, quickly came into focus: Merz Werke from Frankfurt and National Krupp Registrierkassen from Berlin. Interestingly, the latter was a subsidiary of the American NCR! However, following an American decree, a German decision was made in June 1941 to block American-owned assets.

Initially, Merz Werke was to produce the newly designed bolt housing and the attached magazine housing. National Krupp Registrierkassen would manufacture the redesigned grip and frame. Just like Fichtel & Sachs (F&S) and Nüral did with the production of MP38 parts, Merz Werke also stamped their commercial logo on the receiver tube at the beginning of 1940. However, in March of this year they quickly switched to using the factory code “cos”. National Krupp Registrierkassen used the code “cnd” right from the start of production as they probably started later their production. (A strict schedule regulated the assignment of secret production codes)

In addition to the efficiency improvements introduced by the companies mentioned above, an important step to increase production was taken by adding the Austrian conglomerate Steyr Daimler Puch to the list of manufacturers. Initially, Steyr still sourced the receiver tubes from Merz Werke. However, after a short time, Steyr took over the production of all parts, except for the Bakelite components, themselves.

In December 1939, the first manual was published, with the name of the new submachine gun printed on the cover: Die Maschinenpistole MP40. In reality, it was essentially an M.P.38 made from sheet metal. 

Interestingly, while Merz Werke and Krupp National Registrierkassen are typically categorized as sub-assemblers, these two companies produced most of the main parts for the MP40. They were responsible for manufacturing key components such as the pistol grip, the housing, the receiver tube, the magazine housing, and the front sight protector. There is even a batch of MP40s marked solely with the “cos” code on the endcap, which suggests that Merz Werke could also be considered a main assembler.

In addition to the major modifications mentioned, several smaller changes were also introduced during the transition from the M.P.38 to the MP40. These included:

1) A smaller button on the magazine receiver 

2) A redesigned magazine receiver. 

3) A sturdier and longer ejector.

4) A stronger extractor

5) A closed magazine receiver instead of one with weight-saving open slots on the sides, as seen on the M.P.38. 

6) The shape of the Bakelite components was adjusted for the frame and grip of the MP40. These are not interchangeable. 

7) The rear sight was now spot-welded to the receiver tube instead of being screwed on. 

From the very beginning of M.P.38 production, the front sight protector on the barrel included an angular connector that served as an attachment point for a specially designed hinged muzzle cap. This overengineered tool featured a hinged cap at the front, allowing the shooter to pass a chain with an attached cleaning brush through it to clean the barrel without damaging the rifling. On June 19, 1940, it was announced in the Heeres Verordnungsblatt that a simpler rubber muzzle cap would be introduced. This cap protected the barrel from debris and moisture and could be shot through in emergencies without causing accidents. Attempting this with the metal cap would have been disastrous. Steyr implemented this change immediately in late 1940, with Erma and Haenel following in 1941. As a result, many Erma and Haenel MP40s from 1941 still feature this early characteristic.

To prevent the rubber muzzle cap from slipping off easily, a new barrel nut was developed with a groove around its surface, allowing the cap's edge to grip firmly. 

Combat Experiences 

In 1941, significant adjustments were made based on the previous year’s combat experiences and to improve production processes. The M.P.38 was gradually phased out in 1941. Because serial numbers were mixed with MP40 production, it’s difficult to determine exactly how many M.P.38s were produced that year. Assuming production was evenly distributed throughout the year at Erma, we can conclude that M.P.38s were still being made until autumn 1941. To my knowledge, no 1941-produced Haenel examples exist. 

A much larger issue with feeding arose shortly after the invasion of Russia. Prolonged field use exposed the weapons to dirt and fine Russian dust, which mixed with oil to form a thick sludge inside the weapon and magazines. This significantly increased friction within the magazine, leading to frequent blockages. Only the top round could be fired before the mechanism jammed. 

This problem, stemming from a design flaw of the double stack, single feed magazine system by Hugo Schmeisser, prompted an urgent call for solutions. Practical fixes included introducing a magazine brush, banning oiling of magazines, and limiting magazines to 27 rounds. Ultimately, a study by a Mauser engineer led to a design change: adding internal rails to the smooth magazine to reduce friction. All previously produced magazines were retrofitted in a massive recall operation. It is often claimed that the ribs on the new magazines were introduced to strengthen the magazine’s construction. However, the primary reason was actually to prevent jamming caused by dirt buildup.

In March 1942, an official announcement categorized magazines into three types:

1) Type 0: smooth magazines produced before March 1942. 

2) Type A: retrofitted magazines with ribs added after March 1942. 

3) Type B: newly designed ribbed magazines from March 1942 onward.

III.
Modification of the Magazines for the MP38 and MP40

To achieve smoother movement of the cartridges along the inner surfaces of the magazines, two longitudinal grooves are being pressed onto the outer sides of the magazines.

The modification of the magazines is carried out by manufacturing firms.

For this purpose, modified magazines will be issued to the troops as replacements for unmodified ones, without any need for a request.

Since the distribution can only occur as modified magazines become available, requests for preferential allocation cannot be considered.

O.K.H. (Chief of Army Equipment and Commander of the Replacement Army), 25.7.42
— 72b — Jn 2 (IIIb)

In addition to the adjustments to the design of the MP40 mentioned earlier, several less noticeable changes took place. The aluminum barrel protector was gradually replaced by one made of Bakelite, produced by Presswerke AG from Essen.

Furthermore, the middle tube of the telescope spring was now made of rolled sheet steel. This part was also no longer interchangeable with the early recoil springs.

Merz Werke, in addition to the breech housing and magazine housing, also began producing the frame for Erma and Haenel.

A more serious second issue was the hook-shaped cocking handle, the so-called "Wolfszahn" (Wulf tooth) Due to its shape, it had the annoying tendency to get caught on things like clothing, equipment, or other objects. This could cause the cocking handle to be pulled back with the bolt, but not far enough to be blocked by the trigger mechanism. This resulted in a round being chambered and fired, leading to serious accidents.

Initially, a simple field solution was devised, where the cocking handle was secured with a leather strap attached to the barrel. However, this was neither a durable nor a proper German solution. Once again, the German arms industry was called upon to come up with a solution. After some experimentation, Hugo Schmeisser developed and patented a modified, secured cocking lever, which could lock the bolt in the forward position. This required another major recall. Apparently, this was quite a task for the various army units, since at least three official orders were needed from the German high command and the SS leadership to make it happen in 1942, 1943, and 1944. Units in Germany and the occupied territories could order the safety lever from the Heeres Zeugamt and have it installed by the unit’s Waffen-meister.

The reason some M.P.38s and MP40s did not receive the improved cocking lever was that a different arrangement had to be made for the field army. Apparently, this was not done very efficiently, as approximately twenty percent of all MP40s (in my database) produced before 1942 still have the original cocking lever. It is also interesting to note that other submachine guns like the M.P.28, II were occasionally equipped with the same safety feature.

The third design flaw concerned the length of the firing pin. An order in the "Heeres Verordnungsblatt" of November 16, 1942, stated that the firing pin had to be shortened by 0.1 mm. The Waffenmeister had a special tool to measure the exact length.

While the above defects were being fixed in 1942, AEG made another modification. The dark brown Bakelite foregrip was gradually replaced with a more reddish foregrip. In some cases, even the black or brown grip plates were replaced with red hand plates. It is not entirely clear why a change in the composition of Bakelite was made to create this red color. A likely reason could be found in the ongoing search for cost savings or restrictions on certain raw materials.

AEG, which was also a manufacturer of high-voltage switches, used dark red granulate as an insulator. Economically, they may have chosen to use the same granulate for their side products. Identical Bakelite can also be seen in AEG’s hand-powered flashlights.

Steyr seemed to focus more on improving the original model from mid-1942 onward than Erma and Haenel. At Haenel, there was little interest in implementing further improvements. In 1942, only around 25,000 MP40s were produced. Afterward, the production resources were mainly used for the MP41 and later the MKb42, MP43, and MP44.

In MP40s produced by Steyr, it can be seen that from late 1942, the coupling piece in the bolt tube that connects to the barrel was pressed in a different way. Notches were visible on the top and bottom, resulting from hammering the coupling piece into the bolt tube. Apparently, this was successful, as Erma also adopted this method in 1943.

It is worth noting that in 1942 or 1943, Steyr once again sourced housings from Merz Werke, marked with the Waffenamt WaA44. As a result, thousands of MP40s bear only a "cos 42" marking on the end cap. Interestingly, the “2” in the "42" sometimes appears to resemble a “3”, making it unclear which year these housings were intended to represent. 

The observed serial number range for these units spans from 1258h to 7110h, indicating approximately 6,000 produced. All of these MP40s feature the Steyr simplified grip. The reason behind this arrangement remains unclear. It is possible that Steyr faced a shortage of housings and decided to procure additional supplies from Merz. Most other components on these MP40s are stamped with the Waffenamt WaA623. 

During 1943 Steyr made another interesting innovation, originally initiated by Merz Werke. To understand this innovation, we need to go back to 1941. In that year, Merz Werke developed a new prototype of the complete grip. The pistol grip and frame were made from one piece.

Interestingly, this innovation was not immediately adopted for the MP40. However, we do see an almost identical design for the pistol grip on the MKb42 and later the MP43. It was not until late 1943 that Steyr began producing the integral grip for the MP40.

Production continued into early 1944, and a total of around 20,000 MP40s were produced with the integral grip, split between 1943 and 1944. The question arises as to why Erma never implemented the integral grip and always continued using the simple grip from 1940. Perhaps a binding agreement had been made with National Krupp Registrierkassen for several years, preventing them from using the innovation from Merz Werke and Steyr. Or perhaps there were still too many stocks of the open grip.

In other respects, Erma did keep up with modernization. Both MP40s from Erma and Steyr used a simplified barrel nut in 1943. This barrel nut had only two sides instead of six, saving a few steps in production. Another example is that, in 1943, Erma began spot-welding the bolt tube on the outside. Previously, this had been done on the inside of the bolt tube. This change was aesthetically less ideal but saved time. 

Another oddity, seen only on MP40s produced by Erma, is the lack of the rectangular milled cut-out at the rear of the magazine housing on the bottom. This cut-out was meant to make the Waffenmeister's job a little easier, as the ejector could be more easily tapped out from the magazine housing and the bolt tube on models with this cut-out. However, since the improved ejectors rarely broke, Erma deemed this modification unnecessary.

A final change made in 1943 was that the Bakelite barrel protector, which was apparently still not cheap enough, was replaced by a sheet metal version. This can be found on MP40s from both Erma and Steyr. 

Production of the MP40

Much has been written about the production numbers of the MP40. Various authors have made estimates based on acceptance and production records. However, the challenge with these figures is that they rarely provide a clear breakdown of MP40 production specifically. Other submachine guns, such as the MP34ö and the Beretta MP38, are often included in the totals, making it difficult to determine precise quantities. 

As mentioned earlier, I have maintained a serial number database for the MP38, MP40, and MP41 since 2007. My approach is to use this database as a guideline for estimating production numbers. However, relying on serial numbers is not without its challenges and can sometimes lead to confusion. 

One issue is the use of the Sütterlin alphabet in the early years of production, which often results in misinterpretations of letters in the serial numbers. Additionally, entire blocks of serial numbers were possibly and occasionally skipped, as was the case with the P38 pistol. Despite these complications, I have attempted to refine and organize the data as accurately as possible. 

The most significant difficulty I encountered was the simultaneous production of the MP38 by Erma and Haenel during 1940 and 1941. While the "serial number blocks" are evident, it is nearly impossible to pinpoint the exact production or assembly limits for each factory during this period. 

Below, you will find an overview of the production codes and years on the end cap of the housing or lower receiver. Thereafter you find an estimated production numbers, organized by serial numbers, factory codes, and year.

Deployment of the MP40

The MP40 played a key role in the evolving structure of German infantry platoons during World War II. Initially, platoons were large and cumbersome, but after the invasion of Poland, they were reorganized into smaller, more agile 11-man squads. By the time of the invasion of Russia, the MP40 began to replace rifles as the standard weapon for certain key roles due to its effectiveness in close-quarters combat.

Key roles involving the MP40 included:

• Platoon commander: Typically armed with a submachine gun (often an MP40) and a pistol.
• 4 Squad leaders (NCO’s): Transitioned from using a rifle to the MP40 as supplies allowed.

This sums up to a total of 5 MP’s per platoon.

After the invasion of Russia in 1941 another reorganisation took place. The manpower was reduced but the firepower increased. One platoon consisted out of 3 squads of 9 men.

The MP40 was now used by:

• Platoon commander: Typically armed with a submachine gun (often an MP40) and a pistol.
• 3 Squad leaders (NCO’s
• 3 assistant leader.
• 3 soldiers

This sums up to a total of 10 MP’s per platoon.

Source: Avalanche press.

Additional roles

Not only were individual soldiers equipped with the MP40, but it was also integrated into the armament of armoured vehicles. The Heeresmitteilungen 10 from 1942 offers a glimpse into the evolving equipment of these vehicles.

This publication aimed to highlight changes in armaments and equipment.

While the larger scope of these changes is beyond the focus of this website, it specifically mentioned the replacement of the MP18,1 with the MP38. However, by 1942, the MP38 was no longer in production. This reflects the common confusion in official designations, as the MP38 and MP40 were often mistakenly mixed up.

Sd. Kfz. 221:1 MP38, 12 magazines, 2 magazinloaders, 2 six cell pouches

Sd. Kfz. 222: 1 MP38, 6 magazines, 1 magazinloader, 1 six cell pouch

Sd. Kfz. 223: 1 MP38, 6 magazines, 1 magazinloader, 1 six cell pouch

Sd. Kfz. 231: 1 MP38, 6 magazines, 1 magazinloader, 1 six cell pouch

Sd. Kfz. 232: 1 MP38, 6 magazines, 1 magazinloader, 1 six cell pouch

Sd. Kfz. 263: 1 MP38, 6 magazines, 1 magazinloader, 1 six cell pouch

Another example of a vehicle equipped with an MP40 is the Opel Blitz Kfz. 305 (Fernschreibanschlusstrupp motorisiert), used by telegraph teams and outfitted with various telex and radio equipment. In a photograph from the official manual, an MP40 transport box is clearly visible. These transport boxes were designed to carry not only an MP38 or MP40 but also six magazines, a sling, a magazine loader, and several spare parts.

The MP40 was widely used beyond infantry roles, serving in specialized tasks such as motorcyclist reconnaissance and as a self-defense weapon for couriers. It was standard equipment in many vehicles, including armored cars and trucks, and also found use on boats, U-boats, and aircraft, where its compact design and reliability in close quarters proved invaluable. This versatility made the MP40 a key tool across the German military during World War II.