As are the vast majority of 'regular' GI Joe operatives, the team's reservists, or Greenshirts as they're sometimes called, are normal humans - at least, in an anatomical and genetic sense. They're drawn from the U.S. military's elite forces, and thus have exceptional fighting skills.
Bonus Equipment: supplementing the below, standard gear, each Greenshirt will have at least one specialized device to call his own. This is almost exclusively tied to their standard specialty (comm gear for communications experts, and so on).
Helmet: all Greenshirts wear proper head gear while in the field. These streamlined helmets are made from Good (10) m.s. materials, and provide the Greenshirts like protection against physical attacks that strike them on the top or back of their heads.
the Joe-Com: this is a new device given to all Joes since the group's reactivation. This high-tech wristband functions as an audio/video transceiver with various other goodies built in to help a soldier on the go, and is described in greater detail in its own equipment entry.
Knife: standard military issue, every Greenshirt carries a blade with him in the field - and usually at any other point in time. These weapons are made from Incredible (40) m.s. materials, and can be used to cut through items of like m.s. or to inflict Edged Attack damage in melee.
Machine Gun: the Greenshirts usually favor weapons from the M-16 family, for the versatility of accessory mounts. They can fire these weapons to inflict Typical (6) Shooting damage in a single shot, +1 CS in a short burst, or +2 CS in a fully automatic spread.
Semi-automatic Pistol: in the event that their primary weapon is out of ammunition, jammed or otherwise indisposed, Greenshirts always carry a backup piece. They can fire this weapon to inflict Typical (6) Shooting damage in a single shot, +1 CS in a semi-automatic burst of lead.
Bonus Talent(s): supplementing the below, standard skills, each Greenshirt will have at least one additional talent to call his own. This can be anything picked up in the military to date, or even something that these would-be Joes learned before enlisting in the first place.
Guns: in addition to their unarmed combat expertise, the Greenshirts are quite competent in the use of modern firearms. Each Greenshirt may wield any standard, semi-automatic or fully automatic weapon (usually of American design) at a +1 CS to their standard Agility score.
Martial Arts type B: every member of the military is trained in the fine art of self defense - even without weapons, they're a deadly lot! Thanks to this training, every Greenshirt may add a +1 CS to their Fighting when attempting any unarmed melee attack.
Military / United States: all of the Joe Greenshirts possess this skill, as an origin for their other talents for the most part. Regardless of which branch of the military they hail from, each Greenshirt has been trained by the best, to become the best they can be.
As probationary, reserve or trainee members of the GI Joe team, the Greenshirts can consider the Joe team as a contact. They often make good friends with the Joes they are assigned to, and can count these individuals as contacts above and beyond the team (and the military) proper.
The first Greenshirt uniform is a utilitarian affair. It consists of Army green trousers, an Army green, long sleeved shirt over a white T-shirt, brown webbing, holsters, pouches, belts, and gloves, gray wrist, knee and thigh pads, brown leather boots, protective goggles, and their green helmets.
As a whole, the GI Joe team's Greenshirts are presented as highly motivated individuals. They typically stand in awe of the 'real' Joes and, but at the same time are generally highly competent and confident military men and women themselves, often causing a bit of competition between the two.
GI Joe Reservists, commonly known as Greenshirts, are a force of support troops acquired when the GI Joe team was reactivated (again) in the year 2001. This force is culled from the best that conventional military forces have to offer, and can all meet the requirements of the Joe Entrance Exam.
But even with all that, the Greenshirts are not Joes. Not yet. Once accepted into the ranks of the reserves, Greenshirts have to prove they have what it takes to face down Cobra head-on. This involves a lot of supplementary training above and beyond that which they've already endured.
And usually some intimate time with the Joes' most notorious drill Sergeant, Beach Head.
Once they've proven themselves to him, the Greenshirts are given a final exam, which is usually an actual mission that doubles as a live-fire exercise. If the Greenshirts perform to spec (and Beach Head has a very high checklist of qualifying criteria), they get to become 'real' Joes.
No longer Greenshirts, these fellows then get to choose their own code names and join the team proper. Those Joes who are known to have worked through the Greenshirts program are Barrel Roll, Depth Charge, Mariner, and Mayday - though presumably all post '01 Joes had to do so.
The Greenshirt program was maintained throughout the team's second great heyday, and put on hiatus when it resumed a more covert status prior to the outbreak of World War III. It is presumed that these back-up troops were reactivated after the end of that conflict.
And, of course, remain as a part of the post-War GI Joe recruitment plan to this very day.
GI Joe directories featuring a version of the GI Joe Greenshirts: