Intercepting enemy bombers?

[Atahualpa]

I've got a lot of ships guarding my coast. They are all within operational range of fighters that are based in my cities. Yet I get turn by turn attacked by enemy bombers and no fighter ever cared to intercept.

I thought they would intercept if a bomber tries to attack a target within the operational range of it.
The chance for intercepting is 50%. Is this chance calculated for every fighter I have or not?

As I thought be it would have been this:

Enemy->Bomber->AttackSquare(x,y)
Forall (My->Fighters f)
{
    if (!UsedUpList.isPresent(f) && f.canReach(x,y) && f.isOnAirSuperioty())
    {
        if (f.chanceToIntercept > randomNumber)
        {
            f.intercept();
            UsedUpList.add(f);
        }
    }
}

Correct or not?
Any other solution would be stupid anyway

Also I am wondering if the AI can see my submarines with his battleships. I had two subs placed next to his shore and then suddenly came two battleship and killed the two subs
How could that possibly be?

TIA,
ata