after finishing campaign I had around 100 targets done and best/fast way to bomb targets for me was to make a new game and do the first critical mission where u have 5 targets to destroy (2x submarines and 3x ground target) after u bomb the last one, quit to menu, load the game and repeat critical mission. 5 targets in one mission is just great and you can ignore the enemy fighters they wont manage to destroy your bomber :D just dont go back to base its a waste of time and your game will be saved