I don't think WW3 would actually help the US economy. WW2 pulled the US out of the Depression because the manufacturing capacity was there but there wad a crisis of confidence and liquidity. The government pumping tons of money into military spending solved both of those problems.

Nowadays, the US doesn't have enough manufacturing. Even the weapons America supposedly builds are riddled with imported Chinese parts. Go to war with China or any major power and the US Government will flood weapons makers with money but that money has nowhere to go so it'll just drive up inflation even more.