Devan, re: "out of a sudden the enemy got like 50 frigates" -- Like a good human player, the AI saves up cash to buy a dense attack force for a blitz attack. Numbers help when attacking shore guns.
fwiw, As posted a while back, the key to winning is shore guns (artillery). Fill all the slots and shell the enemy ships to oblivion. Ditto for the Hindenburg, tho carriers/cruisers/destroyers/fighters do well against Hindenburg as well.
re: lvl 8, the key to all levels is your shore guns. fill all shore gun slots, use your ships to hold the boss ships in one place, and shell them with your shore guns. for the blimp, use the fortress with anti-air guns, send lots of fighters, and be patient. it's pretty easy to win once you fill your shore guns. and with the fortress, shore guns can shell the enemy base, gradually creeping towards the win.
 "Black Navy War"){kind=icon}
 "Nano War"){kind=icon}