The Heckler und Koch submachine gun, MP-5, is one of the most famous and wide-spread firearms of its class. Its development began circa 1964 under the company designation HK 54. In the 1966, German police and Border Guard adopted the HK 54 as the MP5, and it was originally available in two forms - MP5 with fixed buttstock and MP5A1 with retractable buttstock. Over the years MP5 were adopted by the huge numbers of police, security and military forces around the world, including the German police and border guard, British police and elite Army SAS units, American police, FBI, Navy and Marine Corps, and many, many others. MP5 is still manufactured in Germany by the HK itself, and also licensed to Greece, Iran, Pakistan and Mexico. The only real rival to the MP5 in the terms of proliferation across the world is the famous Israeli UZI sub-machinegun. Most interestingly, the German Army (Bundeswehr) did not adopted the MP5, most probably due to the economical reasons, and turned instead to the UZI sub-machineguns. The success of the MP5 is outstanding. It is based on the high quality and reliability of the gun, great single-shot accuracy (thanks to its closed bolt action), great flexibility and, of cause, good marketing. It seems that no other modern SMG at this time can rival the MP5 in popularity (UZI is not manufactured anymore).  
H&K MP5A3 Sub-machinegun
MP5A3 stock open
       
 
MP5A5 with a 2X night vision scope
MP5A5 with a 2X night vision scope and a silencer
  The MP5 is basically no more than the scaled-down version of the HK G3 rifle. It shares the same basic design with stamped steel receiver and the same roller-delayed blowback action, derived from the post-war CETME rifles. The trigger units are hinged to the receiver and are now available with various fire mode options, ambidextrous or not, and marked with letters, digits or icons. The MP5 is always fired from closed bolt for improved accuracy, but this limits the amount of sustained fire due to the barrel overheating. To avoid this, MP5 cocking handle could be locked in the rear position in the special slot, leaving the bolt in the open position, with no cartridge in the chamber. To commence the fire one must simply release the cocking handle from its notch and then pull the trigger. Modern MP5 submachine guns are equipped with three-lug quick detachable silencer mounts on the barrel. Sights are similar to other HK models, and consists of the front hooded post sight and the adjustable for windage and elevation drum-type diopter rear sight. Special quick-detachable clamp mounts allows for installation of night, optical and red-dot sights if required. Standard magazine capacity is 30 rounds, but shorter 15 rounds magazines are available. Special versions were developed and manufactured in limited numbers during 1980s-90s for the US Law Enforcement market, chambered for more powerful 10mm Auto (10x25mm) and .40S&W (10x22mm) ammunition.

-(Shortened and/or modified version of the article at world.guns.ru)

       
  GAME DATA: MP5A3

A very common version of the MP5. Retractable stock and navy trigger group (safe, semi- & full-auto). Quite accurate and has a good rate of fire at 800 rounds per minute.
Many factions use these. From the Shop to the US Marines and Prometheus.

   
Name: MP5A3  
Slot: 4, sub-machineguns  
Caliber: 9mm  
Capacity: 30 rounds  
Firemodes: Full- and semi-auto  
Accuracy: Good  
   
  GAME DATA: MP5A5

This version is very similar to the A3, but has also a 3 rounds burst option. Standard for the Shops field operatives. Featuring a 2X night vision scope to give the weapon more range and an advantage during night operations.

   
Name: MP5A5  
Slot: 4, sub-machineguns  
Caliber: 9mm  
Capacity: 30 rounds  
Firemodes: semi-, 3 rounds burst and full-auto  
Accuracy: Good  
Other: 2X night vision scope  
   
 
  GAME DATA: MP5A5 SD

Same the A5, but features a silencer to give advantage during night operations and mission requiering stealth.

   
Name: Silenced MP5A5  
Slot: 4, sub-machineguns  
Caliber: 9mm  
Capacity: 30 rounds  
Firemodes: semi-, 3 rounds burst and full-auto  
Accuracy: Good  
Other: 2X night vision scope, silencer  
   
     

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