After the success of the Heckler & Koch G3; the company was encouraged to develop a family of small firearms based off the G3. There were 4 groups of weapons; the first one consisted of a weapon chambered in a 7.62x51mm NATO. The second consists of the 7.62x39mm and the third consisted of a 5.56x45mm NATO. The final group consisted of the 9x19mm Parabellum; which consisted of the MP5, initially known as the HK54.
Still after all these years of service, the MP5 is still going strong and has went through many changes, like the MP5K or the MP5 PDW, but the weapon is still going after all this time.