The American Defense Service or A.D.S. for short is an amalgam of various intelligence agencies and the military. It is a private contractor to the U.S. government and main provider for national security.
The U.S. government changed to private contractors in the 60s to lower corruption. The A.D.S. was amongst the first founded organisations that started out as government funded and got privatized over time. Since each organisation may not have any contracts other than their sole government contract the entire A.D.S. is structured in a way that it handles all matters of national security and investigations. It does not, however, replace the military, it merely works parallel to it. The A.D.S. does not handle international conflict but it does emply espionage tactics outside the U.S.
The A.D.S. launched an investigation into Alvin Severnya and A.S. Industries, the weapons manufacturer for the government. Through clever bending on existing laws Severnya managed to be government contractor and still stay in the private business sector, something unheard of. And then Severnya tried to become the state security cntractor as well by quiring the A.D.S. so an investigation into his business deals was set up.