海 ocean

I flew a giant KITE all the way across the ocean!

Every ocean is full of some damn water (水). think you can remember that one, Einstein?

coast / beach ★★★★☆
海 (ocean) + 岸 (shore) = 海岸 (coast / beach)

the coast OR the beach! Unlike 浜辺 or 浜, 海岸 has a scientific meaning: the coastline, (regardless of if there's sand or not). You'll see 海岸 on maps or geography books. The useage of 海岸 is odd, even for Japanese. Where Americans will just say, "Let's go to the beach!", Japanese might suggest to their pals, "海へ行こう！”（let's go to the ocean!) but ONLY ONCE THEY WERE ALREADY THERE, then they might specifically suggest going to the 海岸 - as opposed to other things to do by the sea. Weird!　

foreign countries ★★☆☆☆
海 (ocean) + 外 (outside) = 海外 (foreign countries)

accross the sea - foreign countries, basically.

navy ★☆☆☆☆
海 (ocean) + 軍 (army) = 海軍 (navy)

in the kaiiiigun, you can sail the seven seeeeas, in the kaiiiigun, you can put yourself at eeeeease...

bottom of the ocean ☆☆☆☆☆
海 (ocean) + 底 (bottom) = 海底 (bottom of the ocean)