At Various times they may carry an oak truncheon, a crossbow, a shortsword... Other weapons known to have been used by watchmen, on the "first thing I could get my hands on" basis, include a siege bow intended to destroy city walls, a small dragon used as a handgun, and another (smaller) watchman.
The police force of Ankh Morpork started off as four separate forces. These were the night watch, the day ward, the palace guard and Cable Street particulars. The early books started to follow the lives of the night watch which was just a few men trying very much to find out where trouble was happening so they could do everything they could to avoid it. The watch was commanded by Samuel Vimes. The night watch saved the city from a huge dragon. After this the watch began to expand and now is a large force with various characters involved.
Sir Samuel Vimes
Captain Carrot
Constable Angua
Sergeant Fred Colon
Corporal Nobbs (Nobby)
Detritus