"Sea Mine Warfare"

Korean War quote about Wonson: “The U.S. Navy has lost control of the seas in Korean waters to a nation without a Navy, using pre-World War I weapons, laid by vessels that were utilized at the time of the birth of Christ.”Rear Admiral Allen “Hoke” Smith.

What happens if a modern nation takes sea mines seriously?

See Chinese Mine Warfare: A PLA Navy 'Assassin's Mace' Capability(pdf) (2009):

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While photos of a first Chinese carrier will no doubt cause a stir, the Chinese navy has in recent times focused much attention upon a decidedly more mundane and nonphotogenic arena of naval warfare: sea mines. This focus has, in combination with other asymmetric forms of naval warfare, had a significant impact on the balance of power in East Asia.

People’s Liberation Army Navy (PLAN) strategists contend that sea mines are “easy to lay and difficult to sweep; their concealment potential is strong; their destructive power is high; and the threat value is long-lasting.”3 Key objectives for a Chinese offensive mine strategy would be “blockading enemy bases, harbors and sea lanes; destroying enemy sea transport capabilities; attacking or restricting warship mobility; and crippling and exhausting enemy combat strength.”

While somewhat dated, the analysis holds true. Mines are easy to lay, hard to clear, and potential show stoppers.