history.state.gov 3.0 shell
history.state.gov
Archived US Diplomatic Documents and Correspondence:
I got letters between various parties arguing about whether a particular ship should be allowed to coal in a neutral port during times of war.
Legal Documents, incl. Treaties.
Full text of Hague Treaties and Rules of War.
www.navweaps.com
Maybe this one is obvious, but a full list of naval weapons with ranges, shell weights, penetration, and usage.
Every ship ever to serve in the US Navy, down to commandeered armed yachts, with pix.
Historic US and Canadian fortifications
www.fortwiki.com
Forts in North America
Welcome to the Caledonian Maritime Research Trust
www.clydeships.co.uk
Specs on every ship ever built in Scotland
A history of Tyne shipbuilders and ships built on the River Tyne
www.tynebuiltships.co.uk
Specs on every ship ever built in Newcastle
Fire insurance plans are often behind a paywall, but they are a killer source if you can find them for free. If you want a building by building layout of your setting at your historical date.