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. However, conditions were not always ideal, and the substations were not really designed to cope with regeneration, which meant that often the train switched to rheostatic braking, where the power was dissipated in a resistance bank. The weight of the equipment was also a serious drawback.