FBI SWAT has the option to carry a target-grade Springfield 1911.
During the gangster/auto bandit era, there is at least one memo documented and viewable on line, where an FBI administrator chastises his men for wanting .45 autos and recommends they stay with the .38 revolver.
The special unit guys were hardline gunfighters recruited for that purpose, but then and now, the Bureau is an investigative agency with a large number of paper pushers.