There are many other versions of the gun, some which use different caliber bullets, are shorter, or have other differences. One important type of MP5 is the MP5SD series, which are MP5s with built in suppressors ('silencers'). The MP5SDs are quieter than most guns and can be used for stealth. The MP5 is used by many special forces groups around the world, including the United States Navy Seals and British SAS.