Just some numbers for thought:
From the merchant marine website:
A pre-war merchant fleet of 1,340 cargo ships and tankers expanded to at least 4,221 U.S. merchant ships by the end of World War II.
Current number of US flagged ships excluding the 81 or so that fall under military command, 182.
From here: https://www.bts.gov/content/number-a...re-world-fleet