In the Second World War the United States was called the arsenal of democracy because the arsenal was real: Ford’s Willow Run built a B-24 on a clock. Kaiser’s yards launched Liberty ships in days. Detroit made tanks. That was not a party central committee. It was companies, unions, engineers, and a government that could buy — not own — the output.
Command economies can mass-produce too, by coercion. The American difference is conversion: a peacetime car plant becomes a bomber plant because the people who know the machines are allowed to solve the problem. After the war those same shops went back to making things customers would pay for.
Socialism treats the factory as a political trophy. The American model treats it as a shop that must work. That is why we could tool up, then tool back, without a famine in between.