C5 is a ship square. All of the unmarked squares in column B and row 6 are water squares.
G are water as well.
All of the squares diagonally adjacent to ship squares must be water squares. The only place for the battleship is F7- I7. If F4 were a ship square, there would be no way to put the third ship square in row 3, so F4 is a water square. The rest of column E is water, so there is a submarine at D1, and another at F9. The rest of A must be the remaining destroyer at A7-A8, so the subs are at D9 and I5.