Basically it’s all a matter of adding up punch and dividing by 6. For every whole number result you get 1 hit, for every fraction you roll the die and attempt to roll below the numerator to score an additional hit.
For instance, 6 Attacking infantry would be 1 hit. (6/6 = 1) but 9 Attacking infantry would be 1.5 hits (9/6 = 1.5 with a remainder of 3.) If you rolled the die and got 3 or less, you round that number up to 2 hits, if you rolled higher then 3 then you only scored one hit.
It’s even more fun in larger battles. 20 Infantry, 10 Artillery, 5 Armor, 5 Fighters, 1 Bomber attacking would be 14 hits. However, in ADS you could range anywhere from 21 hits to 5 hits realistically.
As for SBR’s, it’s a matter of averages. You expect an AA Gun to shoot down 1 in 6 aircraft. So if you did 6 SBRs you would expect your bomber to be shot down on the 6th bomber run. The cost of a bomber is 15 IPCs, so if you lost 1/6th of your bomber every SBR, that would cost you 15/6 IPC or 2.5 IPC. A bomber attacking the factory can do between 1 and 6 damage. The median point between 1 and 6 is 3.5. (1,2,3 on one side, 4,5,6 on the other.) So for an SBR you do 3 damage plus 1 on a roll of 1,2,3 and take 2 damage plus 1 on a roll of 1,2,3.
As for shore bombardment and submarines you usually have to agree before the game if they will be fired as seperate attacks or in conjunction with the main body of the attack. Makes a huge difference. You have a normal attack for individual submarines and battleships shore bombardment if seperate, but if you attack with 2 infantry, 1 battleship you automatically get 1 hit. (1+1+4=6).
