As mentioned before, the MP38/40/41 series are very sensitive to dust and dirt. The main problem is the double stack single magazine feed system which is prone to malfunction or jamming problems when dust and dirt enters the receiver through the ejection port or bolt slot. In order to solve this problem, measures were taken by the "Oberkommando des Heeres" which resulted initially in the leather safety strap for the early style bolt, and later the improved bolt retracting handle.
The Wehrmacht was fighting a war in many theatres in Europe under a lot of different circumstances and experience and field expedient solutions from the combat troops were considered to be very important. As a result, a special message service called "Von der Front fur die Front" was created to communicate inventive and improvised solutions to problems that the soldiers of the Wehrmacht could experience with their equipment.
On the 22nd of September 1944, a message was communicated in the "Von der Front fur die Front" by Unteroffizier Adam Muller in which he explained how you could make a fairly simple protection cover. This message was intended for Ski troops to prevent snow from entering the receiver when they fell. The protection cover was not a field invention of 1944. Earlier pictures taken in the early years of the war prove that the Fallschirmjager units already used similar improvised solutions as can be seen below on these 2 pictures where Fallschirmjager are lining up to board a plane. They are wearing their early 1940/1941 "Smocks" which proves the dating. It could be possible that these early protection covers for the Fallschrimjager units were manufactured by a factory as this often happened for these units. A good example is the so called "Crete Pouch" which was also manufactured in small numbers only, however, I cannot confirm that this was “professionally” manufactured or authorized as standard equipment by the Wehrmacht.
The translated text of the "Von der Front fur die Front" of the 22nd of September 1944 reads as follows:
Berlin, September 22nd 1944
Housing cover M.P.38/40
For Ski- and Mountain troops
The cover (see picture) prevents snow from entering the receiver or the freezing of the telescope spring and guarantees a free operation of the weapon. The cover is easy to make from tent cloth. As closing 3 pushbutton are provided which allows quick removal during combat. The cover is connected to the M.P in front of the magazine receiver with a buckle. The buckle does not need to be opened, it needs to be turned 4 centimeter to the right. So even when the 3 pushbutton are loose the cover cannot be lost. Every unit can easily make these necessary covers for their, by the K.St.N. (Kriegsstärkenachweisung*) allowed, MP's from captured tent cloth. Strong pushbutton need to be used.
Adam Muller, NCO
Fieldpostnumber 07 389 B.
Additional comment: The cover that is described here is well-tested and approved. The MP40 is because of this well protected against snow and sand but still quickly ready for firing. The attached buckle prevents the cover from being lost.
* K.St.N.=Kriegsstärkenachweisung; these were the tables of organization and equipment used by the Wehrmacht.
Below you can see some Fallschirmjagers equiped with the cover:
Today the protection cover or housing cover is extremely rare. If you can find one it's difficult to distinguish and verify it's originality since they originate from an improvised field production. The one pictured below this text supposed to be original sample and is owned by a German collector who is in possession of some very rare pieces relating to the MP series.