Steam Engines and Tenders.

[Puddlejumper]

I know that tenders were switched around as needed on the PRR. I always considered the tender as part of the locomotive, but I imagine the RR considered otherwise. Sometimes it would have been a matter of convenience, other times there could be an operational reason, such as placing a long-haul tender on a recently reassigned locomotive to a long mileage division on the RR. I saw a photo once of a train on horseshoe curve, 2 I1sa (2-10-0) up front with long haul tenders, 2 I1sa pushing the caboose, identical to the road engines except for their short tenders. When built all of these had the same tenders.

dave