 All of the metadyne equipment was subsequently replaced.Despite the shortcomings which led to its demise, the metadyne system as introduced in 1936 on the O Stock trains was the first in the world to provide regenerative braking on an electric multiple unit.Acceleration was smoother than on a train which switched starting resistances, and when braking the metadyne unit returned power to the tracks, which could be used by other trains if needed.