Its pretty obvious what the most lethal weapon is; its mines. But the navy has consistently shortchanged the building of mine clearing ships, aircraft and equipment. Other countries, particularly in Europe, have taken the lead in developing mine clearing technology. In the 1990s, the United States began to invest more money in mine clearing, but dealing with mines is still considered a secondary issue. This despite the danger mines have been, and continue to be. All potential naval opponents of the United States have stocked up on mines. Apparently those who might have to fight the United States Navy have noticed what the most successful weapon to use against American ships is. While mines are largely a defensive weapon, it is a very effective one. And mines can be used offensively as well, if you can get them to places where enemy ships have to operate. Even American counter-terrorist efforts recognize this, at least to the extent that the severe impact of a few naval mines in American ports would have on the economy is recognized. The U.S. Navy may not pay a lot of attention to mines, but their enemies certainly are.
The U.S. Navy has had twenty ships damaged in combat since World War II. Four of them were sunk. For sixteen of those ships, it was naval mines that did the damage Another three were hit by enemy aircraft, and one was hit by a suicide boat bomb. Ten of those attacks, all from naval mines, were during the Korean war, which is where the four sinkings took place. Three of the four Vietnam war attacks were mines (the other was a destroyer hit by a bomb from a North Vietnam MiG-17). During the 1967 Arab Israeli war, an American intelligence gathering ship was attacked by Israeli aircraft (and small warships as well). During the 1980-87 Iran-Iraq war, one American ship got hit by an Iranian mine, another by an Iraqi aircraft firing a missile. During the 1991 Iraq war, two ships were hit by mines, and in 2000, an al Qaeda suicide bomber detonated a small boat load of explosives next to a destroyer.