Simplify the following text for a Grade 6 native English-speaking person.
Original: The MP5 is currently one of the most widely used submachine guns in the world , having been adopted by numerous military , law enforcement , intelligence and security organizations . In the 1990s , Heckler & Koch developed the Heckler & Koch UMP , the MP5 's successor , though both remain in production .
Simplified: The MP5 is a submachine gun made by Heckler & Koch .