For a number of years now, the National Archives and Records Administration has been working to digitally scan it's immense collection of ships plans. It is expected to be a 10+ year project.
Here is a link to the site where they are available for download.
There are many types, not just military, not just US ships either. There are numerous UK tugs and merchant vessels, as well as warships.
There appear to be multiple listings for the same ship, but close examination will show the the plan differs, often due modifications.
Hats off to Umi_Ryuzuki for posting this link on RC Groups.

https://archive.org/search?query=subject%3A%22Ship+Design+Drawings%22