[Graebarde]

841 is a terminal service battalion. Their function is loading/unloading ships at a port or LOTS operation. (LOTS is "Logistics over the shore" such as was the case at Normandy in WW2. They are the stevedore/longshoremen of the army. The battalion would have a HHC which does the planning etc, and from what I read it does not have subbordinate units per se. In the 'old days' this battalion would have attached units, and if a similar unit were deployed to the theater could have units such as:

Terminal service companys which do the actual grunt work and operate the MHE at the port.

Boat companies which operate tugs, lighters and landing craft to assist in the operations.

Truck companies which help clear the ports in theater, though most truck companies are usually assigned to a motor transport battalion.

Within CONUS, much of the stevedore positions are usually filled with civilians, while the HQ would have a mix of military and civilian. In theater, depending on how 'hot' it is and such, the battalion would be staffed with military though the acutal grunt work MIGHT be done by locals they would be supervised by military.

Add on: On further reading I get the impression that ALL these SDDC brigades and battalions are really MOVEMENT CONTROL organizations more than the acutal physical port operation battalions. ie: The 'sister' organization in the Gulf region only has a handful of personnel and is tasked with documentation.

The type of work the stevedore does today is much different than it was nearly 40 years ago when I taught stevedores and traffic managers at the T-school. Not a lot of break bulk movement today with containerization and RO-RO operations the norm.