Could modern forces return to mass mobilization?

Could fleets, air forces, or armored forces again reach Second World War-style numbers?

Yes, after a long conventional buildup; a sustained threat could justify mass production and mobilization even though present forces emphasize smaller elite formations.

Today's preference for small elite forces does not make mass mobilization impossible. A prolonged conventional confrontation, especially one in which nuclear weapons were effectively ruled out, could drive states toward thousands of vehicles and much larger fleets and air forces. Building that capacity would require years rather than an emergency burst of procurement. This is a conditional pathway based on threat, industry, and preparation, rather than a prediction that such expansion is imminent.