[irish1958]

They would guess and fire a shot, see where it came down, then guess again, etc.
When they could "bracket" a ship, they had you and would then pour it on.
It is like putting in golf, or getting to Carnegie Hall. Practice, Practice, Practice!
Torpedoes were another problem, as you couldn't bracket a ship. To reduce error, you would try to get as close as possible and take multiple readings.