The question of how many operating locomotives one needs for an operation is certainly both interesting and necessary to look at. Throwing $400,000 at a loco you don't need when other equipment also needs preserving will make you stop and think. Do you restore an extra loco to run occasionally or do you restore/save 20 pieces of rolling stock or deteriorating structures. You have to have locomotives to run the schedule you have. Cass Scenic in West Virginia requires three operating locomotives. Two to operate to Bald Knob and one to operate to Whittaker. Then you need at least one locomotive under steam as emergency power. Remember we are not talking modern Hondas and Toyotas here we are talking about the railroad equivalent of a Model T. Then you need at least one, if not two, locos that are in the shop, being stripped down to the bare bones and built back up again. So for a hard working operation, scheduling daily operations that needs three locos to meet the operating schedule, you should really have a minimum of five locos, four ready to run and one undergoing maintenance. On an operation like the C&TS having an extra engine at each end of the line to protect the schedule is something we should hope to be able to see in 10-15 years.