Autonomous underwater vehicles (AUVs) promise a radical change in undersea warfare at just the time when conventional technology is becoming less and less affordable throughout the naval world. The greatest threat to warships and commercial shipping is not anti-ship missiles or torpedoes, but rather mines. Potential adversary navies have on the order of 386,000 naval mines –China 80,000; Iran 6,000; North Korea 50,000; and Russia 250,000 – facilitating anti-access/area-denial strategies, while U.S. Navy assessments indicate that a million mines are in the inventories of more than 50 navies world wide.

http://www.sldinfo.com/on-the-cusp-of-an-undersea-revolution-shaping-new-ways-to-deal-with-the-threat-from-mines/