If the tense confrontation with Iran ignites into war, strategists say they expect Iran will strike with thousands of deadly sea mines to try to halt oil tanker traffic and take out American warships. In the shallow, crowded waters of the Persian Gulf, mines pose a sobering challenge. When the U.S. Navy has faced a massive mine threat there in the past, it has failed to protect even its own ships. Now, both Iran and the United States seem poised to fight it out again. Iran has acquired a stockpile...