The HK MP5SD series features at least six silenced versions of the highly successful MP5 submachine gun. The 'SD' in the designation meaning Schalldämpfer, literally translated as "Sound Dampened". This German word is the only differentiation given to the 'silent' cousin of the world's most popular submachine gun. "Silencers" as they are commonly called, both in legal definitions and in popular vernacular do not actually do what their name suggests. Sound suppressed or even dampened is a much better way to describe what actually occurs when a firearm is discharged with one on the muzzle. But they are, with the exception of .22 calibre suppressed guns, far from silent. Sound suppressed firearms are relatively loud, although most can be fired without hearing protection. The key to what the suppressor does, in layman's terms, is to make a gunshot sound like something other than a gunshot. As sound suppression systems go, the SD is one of the more quiet available. The SD suppressor is to my knowledge, the only sound suppressor actually manufactured by HK. Key to the uniqueness of the SD suppressor is that it is coupled with a barrel that has 30 2.5 mm ports that channel the gasses from the propellant, resulting in a subsonic ammunition-firing weapon system. Mechanically, however, the SD series is identical to the original HK MP5 series of submachine guns. The MP5SD is intended to fire standard 9mm ammunition, not special subsonic ammo used by most other suppressed weapons.

The negatives of the SD system are a drop in ballistic performance as well as a reduction in reliability. The SD will definitely start to malfunction much sooner than a standard MP5, due to the amount of fouling that the suppressor forces back into the action.

The six versions of the SD series cover basic changes in the buttstock configuration and the addition of the three round burst capability which is normally not standard in the base models of the MP5 (only automatic and single shot are). When both accuracy and stealth are required, DUTA uses the MP5SD5 (fixed plastic butt and three round burst capability) when both accuracy and stealth are required. For this reason, terrorists throughout the world fear the HK MP5SD.