“the U.S. Transportation Command (Transcom) requirements call for a platform capable of carrying a minimum of 50,000 lb. of fuel for 1,500 mi. It must perform the mission day or night and deliver fuel by boom, hose-and-drogue or both“...
Rather a vague and incomplete requirement - does the platform have to fly 1500nm, offload 50K and then fly 1500nm back? Over what period of time does the platform need to be on station?
1500nm at 500KTAS is 3 hr. Say the burn rate is 5.4 T / hr and alternate requirements are a further hour's burn to tanks dry, then the tanker would need 37.8 T plus whatever time on task was required. With an offload of 50K (22.7 T), that means a tanker on station for an hour would need to have a capacity of around 66 T. Using legacy ex-airline airframes might be a possibility, but the difficult bit would be fitting the boom and associated operator's station.