The Metropolitans, at the time of their introduction, were notable for their rounded ends and quarter-point sliding doors. The cars were fully air conditioned, accommodated only high level boarding, used light weight construction and were built with a top speed of 100 mph and support for Automatic Train Operation. The Metropolitan cars were also the catalyst of change for their respective systems as the high-level boarding required all stations in the electrified zone to be rebuilt from 1966-1968 and the increased power demand forced the LIRR to update its third rail power supply from 650 V DC to 750 V DC to take advantage of the cars' performance. On December 30, 1968 the M1s went into revenue service, with the first revenue train being an 8-car local from Babylon to Penn Station.