Through service Hamptons to Penn Station

I was in engine service on LIRR from 1964 to 1970. I remember being told from oldtimers that in summer through trains from Montauk were operated with steam to Jamaica then change to DD-1s to Penn Sta. After unloading a "backout man" would be on rear end with a "backup hose" and the DD=1s would shove the train through the East River tunnels to Harold then reverse to Long Island City coach yard or Sunnyside Yard. Not sure about originating eastbound from Penn Sta. This would go back a long way. Anyone have information? (prior 1950s)

May have answered my own question. Just came across an old 1950 crew sheet and shows some Port Jeff, Oyster Bay, Ronkonkoma service in and out of Penn Sta weekdays rush hour with engine change at Jamaica. Also Sheffield Milk trains Jamaica to Sunnyside and return. Anyone know how this service (milk) operated?

The extensive book, Steel Rails To The Sunrise, talks about this early operating procedure.

From what is discussed the change from Steam to a DD-1 electric at Jamaica was common practice after the initial period of electrification,
and was used for all steam powered lines.

It goes on to say that after a while the railroad realized it was easier to have passengers change trains at Jamaica, than change engines, and thus
"change at Jamaica" became the norm.

Ken

Would anyone have information on these trains from/to Jamaica for Sheffield Dairies.

Thanks

John Peters