Can battleships see fortified troops?

Only at level three do fortifications conceal their occupants. Your level one fortifications are practically worthless. Even with level 3 fortifications, all if would take is a level one interceptor, armored car, or mot infantry to see what’s inside. If you want to conceal what’s inside a fort, you need to go big. Or go militia, as ships can’t see stealth units.

Thanks!

How do I prepare for an invasion if he does invade?

You're best going with a mix of naval bombers and subs. Naval bombers are prefect for coastal defense. They're the perfect pack hunters. They're cheap and effective against ships (other than cruisers) and ground troops in sea convoy form. You can split them up and fan them out to search larger areas, then if you find anything, recall them to group them up again and send them out after what you find. Subs are also good: for scouting enemy coasts, placing at naval chokepoints, or by your own coastal cities in case someone tries to land on you when you're offline. If you have a premium account, you can even set the subs to attack anything they come into contact with. You can place them in locations only someone with hostile intentions would go and put naval bombers on patrol over them.

With all that said, I'd probably invade you just for using the unit cards.

Thanks Britain also just declared war so...

Send your most worthless unit to his homeland.

I tried it once and my opponent lost some of their core provinces before killing my unit.

Too late I dead

L