I mentioned that in my results. If I remember correctly, 3,333 submarines were lost at sea and the attacker lost 1 destroyer. Now, if you really had those units, the attacker would still have 4,999 bombers and the defender would still have 6,667 submarines, but now the submarines have nothing to attack.
My thinking is if you remove the destroyer, than your bombers can’t hit submarines anymore. Planes can only hit subs if the destroyer is present