If you are not familiar with how military, at least army units are organized, this is how they operate. I suspect for the army at least it has been this way for many years, perhaps being formalized during the Spanish American war of '98. At some unit size, mission needs begin to require individual areas of responsibility. In the Army it begins at Battalion level. A typical Battalion has four major administrative subcommands, in addition to "maneuver" companies, which are further broken down into platoons, and then squads. Battalions are collected together into Brigades, and those into Divisions, those into Corps, and Corps into "Armies." During the World Wars, and Korea, combat units were gathered together into semi-permanent Regiments, similar to later Brigades.
A "Task Force" is a temporary gathering of companies and Battations, usually for a specific mission. Some of our historic Task Forces were TF Smith, the hastily thrown together small unit thrown into battle when the North Korean's attacked. Or the TF sent behind German lines to Hammelberg in a failed attempt to liberate a POW camp. Sadly, on their way back, they stopped for a few hours, no realizing they were down range on a German Panzer tank range until dawn came.
In American history, TF's were usually were decimated in heroic attempts at some desperate mission.
Breaking down Army command structures, at the Battalion level there is S1, personnel; S2, intelligence; S3, Operation; and S4, logistics. At Division level, these are "G" groups. Everything an army command does is in one of these sub-commands, with the exception of the War Fighting units, which are under the control of the HQ group. At really high levels, sometimes there is a G5, a political command for dealing with a foreign nation's government.
Unique to Special Forces Companies is also a S1, 2, 3, 4 structure, as a SF company is capable of independent operation. For instance, as an A Team Comander, I was also the S1 of our company. When I was first assigned to my SF company upon my return from Vietnam, S1 was handled by the Sgt Major, who along with the CO was drunk on George Dickel by mid afternoon.
Later, under our new Commander, a Mormon Major, a New Sheriff In Town, he told me our company was about to undergo a big inspection, and our S1 area was a total disaster, and told me to get it ready. We soon passed with Flying Colors.
So.... Our EVAC hospital had the same four sub commands, although not called "S" this or that. Our S1, or personnel chief was a young female Captain. Here handling our mail too, passing out packages to several of our troops. She had enormous responsibilities, and I did not know until we were home later that her husband had deserted her just before we deployed. What an awful thing to have to deal with.
Mail was slow both ways. More about that later. Wherever this young Captain is, all of us owed her a lot, and I hope she found happiness and a good life. A lot of us were replaceable, but she most certainly wasn't.
I'll talk later about how mail and packages were in another post.
All the best... SF VET