Ships are fantastic for moving bulk goods between countries.
I would guess they are not so useful in wartime because missiles and torpedoes are a lot cheaper than ships.
Plus ships can no longer use obscurity for security against large countries: modern satellites and floating drones will dox em quickly.
No idea about submarines: but extrapolating from knowledge of what is possibly with physics, I wouldn't want to bet I could hide em from any high tech country.
I would guess they are not so useful in wartime because missiles and torpedoes are a lot cheaper than ships.
Plus ships can no longer use obscurity for security against large countries: modern satellites and floating drones will dox em quickly.
No idea about submarines: but extrapolating from knowledge of what is possibly with physics, I wouldn't want to bet I could hide em from any high tech country.
Disclaimer: I'm sitting in an armchair.