If the USA gets into a global war, where they need a large number of convoy ships, where are they going to get them ?
That exact point is getting discussion on the “What’s Going On With Shipping” YT channel.
That said, we moved a LOT of stuff in the Gulf Wars.
The even bigger situation you speak of would be a grind it out land war with China. Highly unlikely.
Where they got them before. In WW2 transport wasn’t just by US or allied flagged ships. These were civilian ships chartered for particular voyages. A ship sailing into dangerous waters would be required to sail in a convoy.
they’ll just declare sanctions against a country with some ships and steal them.