At the time of timetable revision in October 1978, JNR tried to increase the transportation capacity during commuting hours by organizing two sets of seven-car trains with an extra set of four-car train (total eighteen cars), composed of newly built cars plus existing cars like the extra trailer coach on the Osaka Loop Line, a used Tc transferred from the Yamanote Line and an extra car from Akashi Depot.
1978年10月のダイヤ改正の際に、新造車と大阪環状線の予備T及び山手線の中古Tcに明石の予備車を活用して7連×2本+予備4両1編成（計18両）を編成、通勤時の輸送力増強を図った。