Just cannot finish as unable to sink all destroyers after many attempts. Any help for an old guy?

theres 3 types of ship:

the small ships, the bigger ships and the carriers.

You don't need to ditch a full bomb load on the small ships, only drop 2 bombs and they'll sink. The bigger ships need 4 bombs to sink and the carriers need about 4 to a full bomb load (6 bombs) dropping to sink it.