The Elite Forces has two primary divisions. As Starfleet has the divisions of Command, Science/Medical, and Operations/Engineering, we have two divisions: The Advance Guard Teams (aka TAG Teams) and the Science, Technology, and Engineering Maccabees (aka STEM Maccabees).
TAG Teams are the warriors who take direct action to protect and defend the Federation. They are the covert operatives who are more like the Special Forces teams of yesteryear. They are the ones who must endure the most strenuous physical training and be ready to launch for a mission at the drop of a hat.
STEM Maccabees are the best and brightest of Starfleet's medics, scientists, engineers, and technologists. They research and create the new medications and medical procedures, technology, equipment, and weapons that are used by the TAG Teams in the field. Before the mainstream Starfleet vessels receive these advances, they are imagined, created, prototyped, and field tested by the Advance Guard. Some of the technologies that we have sent down the line are the Type 9 and 10 photon torpedoes, tri-cobalt torpedoes, and phaser cannons. Our phasing cloak, multi-layer defense shields, and much more remain exclusive to the Advance Guard for now.
STEM Maccabees are also responsible for discovering critical information about the threats we encounter such as learning about the biology of new hostile races and how to counter more advanced weaponry that may otherwise defeat our current defenses.
Within the Advance Guard, we wear the same uniforms as those of mainstream Starfleet: red for Command, yellow for Operatons/Engineering, and blue for Medical/Science. There are very few ways to tell the difference between a "Fleetie" and a member of the Advance Guard. One is by the eagle collar pin worn on their left uniform collars. The other way is the different combadge that is issued to the Advance Guard members. The Fleeties will wear their gold delta shields in various designs. We use a silver and black combadge instead, symbolizing the shadows within which we work (the black) and the fact that we strive to disappear into the woodwork by not being showboats (signified by the less extravagant silver in place of the gold).
When one joins the Advance Guard, he must choose a division if he has not already done so while a mainstream Fleet member. This determines what billet he will pursue and where he will fit into the organization (as well as the color of his uniform). This is not a permanent choice: one may transfer between divisions as desired, provided that such a billet is available when the transfer is requested. However, most remain within their chosen divisions for their entire careers. If one cannot easily decide, he should ask his recruiter or the Command Staff of his ship for guidance. They will be happy to assist.