Bomber Crew

The Final Mission was not too difficult in my experience, but I had a very specific operating procedure by the time I had reached this portion of the game.

My set up:
Early on I replayed various blue target missions to eliminate Enemy Aces and to take out extra targets towards my 200 needed, this allowed me to have winter gear for my entire flight crew, a highly upgraded bomber and to have almost the entire crew leveled up with extra skills and had multiple crewmembers able to perform the same task in case of an emergency.

That being said, I rose to high altitude, and with my navigator using the stars I flew the entire way there (and back) above the Nazi defenses and defenders. Once I had reached my destination while I passed over the target, I had my radar operator call in Spitfires, tagged all enemy fighter plans and once I had some distance from the target then turned and emergency dived to mid altitude. I had four fully leveled up gunners (including my bombardier) blazing away while I lined myself up, then quickly had my bombardier drop from his turret and release the bomb. Immediately, climbed for high altitude and cruised my way back over all the enemies and defenses that tried to catch me.

So, the winter gear was a must, high/full level crew made for an easy bombing run, and a strong, high capacity plane made this mission possible for me to blow up the bunker on my first try. Hope you have a similar experience and have had fun playing this great game.

Good luck!