Simon Whistler explained the purpose of a train’s caboose and why they are no longer used in an episode of his always informative series Today I Found Out.
Carrying a brakeman and a flagman back when brakes were set by hand, when it was time to slow the train, the engineer would blow the whistle. This signaled to the brakemen, and one would emerge from the caboose and work his way toward the engine, while another would leave the engine and work his way back toward the caboose. At each car, the brakemen would stop and turn its brakewheel with a club. Once the train stopped, the flagman would leave the caboose with a flag, lantern or other visual display and walk back down the track to warn any approaching trains.