For F-Day, here's my strategy.
The sea battle. Start off with purchasing a destroyer and move it north-east. Move your existing destroyer north to engage the enemy destroyer. It'll take 2 shots/turns to sink the enemy. Do the same with the 2nd enemy destroyer further to the west. Use your brand new destroyer to inflict maximum damage. After you've taken out the 2 enemy destroyers, position both your destroyers close to your shipyard. The enemy will try to deploy ferries to transport their troops. It's tempting, but try not to attack the ferries when they're empty. Only attack when it's loaded with infantry. Later on, the enemy will deploy one more destroyer. Feel free to purchase another destroyer to take it out. Alternatively, one of your existing destroyers may have upgraded so you can use that instead. Be careful of enemy grenadiers on the coast. They have pretty good range, so stick to your side of the coast unless you're attacking loaded ferries. Always attack and then retreat.
To defend against the waves of grunts and engineers coming from the south, I use 1 sniper and 3 grunts. Position your sniper and 1 grunt on the platform located just directly south of your base. Place the sniper south of the grunt. Your other 2 grunts can be placed next to that bush west of the platform. Just keep your 4 guys right there and you'll easily hold off the assault from the south. Don't try to advance south.
That's it for defense. Now, for capturing the enemy base.
I like to send 2 infantry teams to the enemy island to cover for my engineer. On the enemy island, there's an elevated platform in the north. I put 2 snipers there.
From the south I'll have a team approach the enemy barracks led by 2 grenadiers and 2 grunts.
After you've cleared the path to the enemy barracks, you can position your 2 grunts by the barracks entrance. They'll trap any enemy infantry at the entrance while your engineer makes a dash along the north coast to capture the enemy HQ.
