It will take USN and Pentagon about 2yrs to figure out WTF is going on, and another year or so to implement a countermeasure. USN has some minesweeping, but not for those sort of mines, mostly focused on advanced sea-floor sitting basically "sleeper cell torpedo" in shallow water in small but important sea lanes. Most minesweeping now going to LCS program, and how its that working out?

https://en.wikipedia.org/wiki/Battle_of_Tassafaronga
The US navy commander ordered his line of cruisers to stay in line as they were getting rekt by Long Lance, because (even after Pearl Harbor) he didn't believe the Japs would have any weapons USN didn't have. He kept his command by lying about amount of damage he inflicted on enemy, plus his connections in WashDC. That dynamic hasn't changed, just gotten worse. Traditionally, it takes the USA about two years to start putting competent people in charge.