Goldmark Whales

So in one of my fights (I don't have the screenshot sorry), I spent days making up a elite army group with 7 battleships, 5 light cruisers, and loads of artillery, cavalry, tanks and infantry, and just when I was sailing back to my territory, my entire progress was gone with a whale who spammer 20 battleships out of thin air, I put a balloon and spy there to check before I even put my army there, and my entire fleet was destroyed. That was like the chunk with the best forces in my entire army. What should I do now????

Btw can someone tell me how to counter gm whales