The UNSC Special Forces are the special warfare branch of the UNSC Defense Force [1].
Units
SPARTAN
SPARTANs are the most skilled and disciplined soldiers available to the UNSC. They take part in intense training at an early age, with the later two programs adding enhancing MJOLNIR and camouflage armor, making them extremely skilled in combat.
Below are all known SPARTAN squads and companies.
Many UNSCDF personnel were part of the ORION Project, specializing in covert operations, assassinations, and conducting high-priority, high-risk operations against enemy forces. Numerous units are under the supervision of Section Three within the Office of Naval Intelligence, which coordinates their special operations missions; one such unit are the members of the various SPARTAN-II teams.
Orbital Drop Shock Troopers
The Marine's Orbital Drop Shock Troopers are an important part of any UNSC invasion force. Disciplined and skilled, they drop into the most hostile areas via HEVs. They attempt to complete some of the most difficult tasks in hostile areas, such as clearing enemy ground forces or establishing a landing zone for incoming Pelicans.
Below are the known ODST units.
Sources