The Heckler & Koch MP5-A4 is a weapon used both in the Elfen Lied manga and anime series, but most especially the latter, a favored weapon of both the short-lived security forces from the Diclonius Research Institute and the late-episode members of the Special Assault Team. This weapon proved effective when surprising a single attacking Diclonius but much less so when facing down Lucy. It is a sub-machine gun developed in Germany in the 1960's, and widely used by special, security and secret forces throughout the world.