Well we used to be able to crank a ship out in a month. 4 years to make a medium sized ship, sad.
That's been par for the course since World War II.
We also used to have dozens of sources for building our ships. Right now we have one shipyard for carriers, two for submarines, two for destroyers, and one for amphibious ships like the New York. Hard to crank them out faster under conditions like that.