Butei (武装探偵, Busou Tantei, lit. "Armed Detective"), is a national qualification created to combat the worsening crime rate. The Butei are allowed to bear arms and arrest people. They'll take on any job for money, so long as it falls within the "Butei Law".
The training facility is in Tokyo Bay for the unique purpose of training Butei, Tokyo Butei High School nicknamed "Academy Island".