Wikipedia
The black gang are the members of a ship's crew who work in the fire room/engine room; they are also called stokers or firemen. They are called "black" because of the soot and coal dust that is thick in the air in the fire room/engine room. The term began being used in the days of the coal-fired steamships. The term is commonly used in the United States Coast Guard and United States Navy to describe personnel in "M" and "B" divisions.
Usage examples of "black gang".
It took years for me to figure it out, but what it really meant, as an omen or conjure, was that she was basically just like the women of the black gang leaders on the South Side, even if she was an Indian.
Two teen-age boys from their neighborhood entered the car: black chinos, black shirts, black gang jackets with PLAYBOYS lettered in dripping red on the back.
Then, reflecting on the night watch above him on the Texas deck, the black gang down below in the engine room, and most of the folks in the staterooms being the type to call ports on a steamer windows, he realized it only stood to reason a more experienced traveler would get to hog such comfort as there was aboard this tub on such a muggy night.
These are the only firerooms left in the Navy where the black gang has to work under air pressure.