Warships built farthest from the ocean

Which warship was constructed farthest from the ocean?

Great Lakes warships from the War of 1812 are the main suggestion, with Paraguayan monitors added later; the exchange does not establish a measured record.

Great Lakes construction during the War of 1812 is the leading suggestion for substantial warships built far from the ocean. The category excludes a tug or patrol craft simply fitted with a gun. The definition of ocean also matters: a yard on the Black Sea or Baltic is already on a sea, even if far from an ocean coast. Paraguayan river monitors are suggested in a follow-up. No measured distance comparison or single named winner is established.