The campaign plan calls for many coastal minelaying submarines before the next war. With 116 ships under construction and a projected submarine force of about 380 boats, the minefields should accumulate quickly. A large minefield will not necessarily stop a port attack. It can inflict losses and add uncertainty, raising the cost enough to alter an opponent's decision.
Notable Point · 19:00-21:48
Mines make a port attack costly rather than impossible
A coastal-submarine build plan is used to explain how minefields can raise the cost of attacking a port.