You will do all yours and then I'll do all mine. (The only thing we alternate is placing aircraft.) Damage takes effect at the end of the phase after we both fire. You can do them all in one mondo post or one at a time - but if you do many together, just indicate your second choice in case you have already sunk the first target - so it might look like this:
Yamato mains against Arizona Yamato secondary against Arizona (or Lexington) Yamato tertiary against Arizona (or Lexington or Hoel)