The Fusō
Those of you who studied the Japanese warships in the game, you'll know that the Tone is in fact a heavy cruiser and not a battleship. Unfortunately your pilots are slow on the uptake, and it's only after the Tone is sunk do you realize that you were attacking the wrong target. The Fusō, a fully-fledged battleship, is coming in "to pick a fight with the Lex".
You lose control of Donald at this point, but you gain control of the Lexington. Half-control, more like - you can't steer her or change her speed, but you can have her launch squads of planes. The Fusō is to the north and is attempting to bear down on you. You have a single destroyer as an escort, but you can't control that either - the enemy has the Fusō, two destroyers, and six Zeroes in the air.
Regarding the Fusō, she'll try and chase down the Lexington, but you have the head start, and so the Fusō can't catch up. However, once Lexington hits the eastern border, she'll turn around and head west - straight for the Fusō. You have to sink the Fusō before that happens. Basically, there is a time limit, but it's hidden.
Start with the Zeroes - they're the biggest threat to your bombing wings. Have the first two squadrons consist of Wildcats and the second two consist of SBDs. Send the former at the Zeroes, and have the latter target the two destroyers - one squad of three SBDs for each destroyer. This should be more than enough to sink it.
The Wildcats arrive on scene first since you launched them first, so switch to the Wildcats and prepare for some real dogfighting (Donald had a super Wildcat as a one-of-a-kind heroic unit). Mix it up with the Zeroes just like before, only the seas are against you. The destroyers should fire some flak up in the air, but ultimately it shouldn't do much aside from annoy you. Make short work of the Zeroes, and once both squads of Zeroes are down, have all the Wildcats retreat to the carrier. In the event squads of Wildcats get downed, replace them as quickly as possible.
Once the Wildcats are done, your SBDs should be in bombing range shortly. They'll fly over the destroyer they're targeting, then initiate their dive. As with the previous SBDs, follow your squad through the dive and target each ship's weak spots - the ammo magazine or the fuel tank. As soon as your squad is done with their bombs, they'll automatically receive landing orders and head for home.
Your first wave alone should have neutralized the six zeroes and both escort destroyers, paving the way for torpedo bombers. Destroying the destroyers also fulfills the mission's sole secret objective. The moment all your planes are back, have all four wings of aircraft consist of TBF/D Avengers. Battleships have high deck armour, so dive bombing is much lses effective, and the battleship is immune to machine gun fire. Despite this, when flying a torpedo bomber, pepper the machine guns of the battleship with machine gun fire to silence them as you make your approach. Drop the torpedo at point-blank range and hold the trigger to confirm your hit.
Continue launching torpedo bombers until the Fusō is no more. It should sink after about three or four wings of torpedo bombers (or possibly more depending on your difficulty level).
Regarding the Fusō, she'll try and chase down the Lexington, but you have the head start, and so the Fusō can't catch up. However, once Lexington hits the eastern border, she'll turn around and head west - straight for the Fusō. You have to sink the Fusō before that happens. Basically, there is a time limit, but it's hidden.
