to sink a battle ship
 

i attacked a battle ship with 8 helldivers each carrying 2000 pounds of bombs and i saw hits but the ship didnt go down ,what does it take to sink one ?

Big ships are tough. Maybe it will sink if you hit the waterline.

Our testing indicated a while back that three fully laden mosquitos with 2000lb ordnance can destroy a BB if they all skipbomb and successfully hit the hull midship.

Ships have a very limited damage model. They are parted into sections from front to aft, at least three. IIRC you can sink any ship by hitting the port or starboard front area by 2000 kg worth of ordinance(skip bombing). May even work with port or starboard aft. Center section usually needs more. Smaller ships take less - might have been 1000 kg for CL and CV, DD needs 500 kg.
Damage in different sections does not add up. You can get a lot of non lethal hits on a BB with 2000lbs that way, if center section can withstand 2 hits you can get at least 8 hits - and it may be that you have more than three sections for larger ships, maybe five, then it could be that up to 20 hits that do not sink the ship. Any damage seems to add up, so it is possible to sink a DD with 10 100 pound bombs.

Try hitting the front section - it will take only two hits.

I remember that in earlier versions (before 4.09) it was possible to sink a battleship or a carrier with one 1,800-2,000SC in dive bombing. Don't know if that is possible today.

sink bb
 

how many US torpedoes MK13. hit's are needed at the front section to sink one.

Our testing indicated three torps needed, but all hits (again) were registered midship

Skip bombing is more effective than dive bombing against big ships. A fully loaded F4U can take out a battleship in two skip-bombing sorties, maybe even one if I remember correctly.