▁The ▁Ok hot sk ▁service ▁was ▁first ▁introduced ▁by ▁Japanese ▁National ▁Rail ways ▁from ▁the ▁start ▁of ▁the ▁re vised ▁tim et able ▁on ▁ 2 2 ▁September ▁ 1 9 5 9 , ▁as ▁a ▁semi - express ▁service ▁operating ▁between ▁ ▁and ▁, ▁using ▁Ki Ha ▁ 2 2 ▁ 2 - car ▁DM Us , ▁with ▁five ▁return ▁work ings ▁daily . ▁From ▁July ▁ 1 9 6 0 , ▁services ▁were ▁extended ▁to ▁S app oro , ▁and ▁ran ▁couple d ▁with ▁S ō ya ▁semi ▁express ▁services ▁over ▁the ▁H ak od ate ▁Main ▁Line . ▁ ▁From ▁the ▁start ▁of ▁the ▁re vised ▁tim et able ▁in ▁October ▁ 1 9 6 1 , ▁services ▁were ▁upgrad ed ▁to ▁" Express " ▁status , ▁and ▁were ▁operated ▁using ▁Ki Ha ▁ 5 6 ▁ 4 - car ▁DM U ▁form ations , ▁including ▁a ▁Ki Ro ▁ 2 6 ▁Green ▁( first ▁class ) ▁car . ▁ ▁From ▁the ▁start ▁of ▁the ▁re vised ▁tim et able ▁on ▁ 2 ▁October ▁ 1 9 7 2 , ▁services ▁were ▁upgrad ed ▁to ▁" L im ited ▁express " ▁status , ▁and ▁were ▁operated ▁using ▁Ki Ha ▁ 8 0 ▁series ▁DM U ▁form ations . ▁ ▁From ▁the ▁start ▁of ▁the ▁re vised ▁tim et able ▁in ▁November ▁ 1 9 8 6 , ▁the ▁Ki Ha ▁ 8 0 ▁series ▁rolling ▁stock ▁was ▁replaced ▁with ▁Ki Ha ▁ 1 8 3 ▁series ▁ 6 - car