In the late 1970s, the Delaware & Hudson started yeeting their still-large fleet of 244-equipped locomotives. But a fistful of RS-3s had their 244s dealt with in the tradition of the TdM shops (but not by shipping them to ILW; instead they were sent to Boise, Idaho to be rebuilt into MK TE56-4As) of yanking the 244 and wedging a 251 into the now-empty engine compartment.

Some of the units were repainted into various experimental schemes, but by the mid 2010s they had all gone back to their original d&h paint schemes (including 506’s bicentennial paint.

In the mid 2020s, most of these now-elderly locomotives were sent to ILW to be rebuilt with low-emissions prime movers. The entire drivetrain was removed and replaced with a Cummins QSK50 powering an AC drivetrain, which was so much smaller than the 251 was that ILW simply scrapped the existing long hoods and installed eco-425rs ones in their place. And with that done the low short hoods were cosmetically modified to have the same profile (but longer) of the eco-425rs low short hood, and when the new control stands were put in the cab windows were replaced with newer centered two-pane units. (So if not for the Alco cab & road numbers you might think this was just another eco-425rs.)

The only DL15 that was not remanufactured by 2026 was the D&H’s ex-bicentennial unit (#506), which is being used as the Northeastern District’s US 250 commemorative diesel locomotive.