CRAF and STUFT
US paid in 1970s to convert PanAm/TWA 747-100 to pax/freight QC, remaining in airline operation under an annual retainer equating to weight increase/operating cost pain. Civil Reserve Air Fleet tails were then liable to short-notice call-up in military exigency. World and other DC-10QC similarly.
UK MoD has open-door, on-call charter General Terms Agreements to access defined hulls at very short notice; no delaying tender process, rates all pre-sorted. Heavylift Belfast was a case; weird Antonovs now ditto. The maritime phrase is Ships Taken Up From Trade.
Rest is conspiracy. UK or French Defence budget-holders are not in the business of hand-outs to shareholders - in BA's case foreigners exceeded 51% of equity many years ago.