A martial art called Sambo.

Assuming "troop" is referring to a military unit...

All Russian military personnel learn the combat brand of Sambo (a martial art developed in Russia). Russian special forces are collectively called Spetznaz - this includes all types of special forces from military intelligence to Navy Seal-type soldiers. At least some spetznaz receive a greater degree of training in Sambo than army regulars. Sambo is regarded as a formidable martial art in combat and in sport-fighting (MMA, etc.).

The military does not utilize one specific martial art that exists outside of the military. The green berets will have undergone training in grappling as well as striking, disarming and other CQC (close quarters combat) techniques. Note that their training is not oriented towards winning tournaments, fighting with gloves, or just roughing up some guy at a bar - they are trained to kill, disable, submissify.

The closest single styles of martial arts to what the American military uses (at any given level) are Krav Maga and Sambo (which are related). Krav Maga is the martial art that was developed and is utilized by the Israeli military (standard and special forces). (Combat) Sambo is the martial art that was developed and is utilized by the Russian military (standard and special forces). There is also sport Sambo, which is obviously different.

it's called sambo.