The SWAT team are infantry units that appeared in the campaign.
The SWAT team appears mainly in U.S. Army centric segments like Operation Rushmore protecting key sites from the Consortium and the Assault on JFK airport where they were able to take back JFK airport and protect then Vice-President Cardiff from a terrorist assault.
A SWAT infantry unit can be spawned by entering "swatatyourorders" in the secured line box. And as far as Elite infantry goes, SWAT infantry are somewhere in between the Task Force Commando and the Delta Force.
"Duck for cover!"