The U.S. and over 30 other nations recently held a joint mine clearing exercise, called the International Mine Countermeasures Exercise 2012 (September 16-27). The numerous training events were directed at dealing with Iranian attempts to block the entrance (Straits of Hormuz) to the Persian Gulf. Iran insists it will have no trouble doing this and blocking the export of oil. Some 35 percent of the world's oil shipments pass through these straits, which comes to about 15-20 tankers a day (plus a dozen or more non-tankers). The Persian Gulf, in general, is a busy waterway. It is 989 kilometers long and the average depth is 50 meters (maximum depth is 90 meters). Naval mines are Iran's best bet if they want to shut down the straits.
The Iranian problem is that they have a small navy, an obsolete air force, and a poor track record when it comes to shutting down tanker traffic in the Persian Gulf or the Straits of Hormuz. They tried once before, in the 1980s, when they were at war with Iraq. The two nations began attacking each other's tanker traffic early on, in an attempt to cut off each other's oil sales (and, thus, military purchases). Iran didn't want to shut the Straits of Hormuz because it needed the oil revenue more than Iraq (which was getting billions in aid from other Arab states) did. So each country concentrated on attacking shipping in the Persian Gulf. Over 500 ships were attacked, 61 percent of them tankers. Only 23 percent of the tankers attacked (mainly with anti-ship missiles) were sunk or immobilized. The attacks, using fighter-bombers and warships, only hit about two percent of the ship traffic in the Gulf. Iran lowered its oil prices to cover the higher cost of ship insurance and, in 1986, Russia and the United States intervened to protect Kuwaiti and Iraqi tankers (which were taking most of the damage).
The Iranian military is in worse shape today than it was 25 years ago and would not last long trying to attack ships. That leaves the Straits of Hormuz. This is actually a wide (about 30 kilometers) deep channel. Normally, shipping sticks to narrow (a few kilometers wide) channels, going in and out, to avoid collisions. The main Iranian threat has always been seen as naval mines. The Arab states have a lot of mine clearing equipment and more numerous air and naval forces than Iran. In addition, there are the United States and NATO forces in the area. The problem was that all these mine clearing forces had never practiced under realistic (wartime) conditions. In short, what would everyone do if Iran did mine the straits.
Iran would probably mine the straits if sanctions, or military action, halted all Iranian oil exports. Otherwise, mining the straits would be economic suicide. If Iran tried to shut down the Straits of Hormuz, it's more likely that effort would fail and the straits would remain open for non-Iranian oil. With the loss of their oil exports, Iran would find its remaining military forces being hunted down and destroyed day after day. Not only would Iranian oil exports be halted but so would imports. Iran depends on imports of food (over 100,000 tons a week) and gasoline to keep its economy operating.
For an Iranian mining attempt to work they would have to get the mines onto the bottom of the straits and then prevent the rest of the world from clearing those mines. That would be difficult, as will Iranian attempts to plant additional mines. Such attempts would not be impossible as Iran has small submarines and speed boats along with sailors willing to carry out suicidal missions to deliver the mines. Even that may not be sufficient, as this sort of fanaticism failed against the Americans in the 1980s. While Iran has worked to overcome their shortcomings, most of the solutions appear to be publicity stunts mainly meant to make the Iranian population feel better.
Meanwhile, the mines are a serious danger. While often ignored, naval mines are a formidable weapon. But they just don't get any respect. The historical record says otherwise. Modern naval mines were widely used for the first time over a century ago, during the Russo-Japanese war (1904- 1905). These were contact mines, floating in shallow water and kept in place with an anchor and chain. When the tide was right they would be just below the surface, ready to explode whenever struck by a ship. Some 2,000 of these mines were used to destroy sixteen ships during the Russo-Japanese war. That's one ship lost for every 125 mines used.
During World War I (1914-18), modern mine tactics were developed still more. Thousands of mines were laid to provide defensive barriers against enemy movement in the North Sea. Mines were used offensively by secretly placing them across known enemy sea routes. More than 1,000 merchant and war ships were lost because of the 230,000 mines used. That's over 200 mines used for every ship lost. During World War II there was a major effort to develop better mine clearing methods. During World War II a total of 2,665 ships were lost or damaged to 100,000 offensive mines. That's one ship for every 37 mines. Some 208,000 mines were used defensively to inhibit enemy movement and tie up his resources.
Naval mines achieved several striking successes during World War II. In the Pacific naval mines proved more destructive to the Japanese war effort than the atom bombs. During a 10 week period between April and August 1945, 12,000 mines were delivered by American bombers. These destroyed 1,250,000 tons of Japanese shipping (670 ships hit, 431 destroyed). That's 18 mines for each ship hit. The Americans had air superiority, so losses during these 1,500 missions amounted to only 15 planes, most of them to accidents. Had these missions been flown against opposition, losses would have been between 30 and 60 aircraft, plus similar losses to their fighter escorts.
A conventional submarine campaign was also waged against Japanese shipping. Comparisons to the mine campaign are interesting. A hundred submarines were involved in a campaign that ran for 45 months from December, 1941 to August, 1945. Some 4.8 million tons of enemy shipping was sunk. For every US submarine sailor lost using submarine launched torpedoes, 560 tons of enemy ships were sunk. During the mine campaign 3,500 tons were sunk for each U.S. fatality. On a cost basis the difference was equally stark. Counting the cost of lost mine laying aircraft (B- 29's at $500,000 each) or torpedo armed submarine ($5 million each), we find that each ton of sunk shipping cost six dollars when using mines and fifty-five dollars when using submarines. This data was classified as secret until the 1970s. It indicates that mines might have been more effective than torpedoes, even if the mines were delivered by submarine.
The Germans waged a minelaying campaign off the east coast of the United States between 1942 and 1944. Only 317 mines were used, which sank or damaged 11 ships. This was a ratio of 29 mines used for each ship hit. In addition, eight ports were closed for a total of 40 days. One port, Charleston, South Carolina, was closed for 16 days, tying up not only merchant shipping but the thousands of men, warships, and aircraft dealing with the situation. American submarines also waged a limited mine campaign in the Pacific. For 658 mines used, 54 ships were sunk or damaged (12 mines per ship). No subs were lost. Considerable Japanese resources were tied up dealing with the mines. On the Palau atoll the port was closed by the mines and not reopened until the war ended. Even surface ships were used to lay mines. Three thousand mines were laid by destroyers. Only 12 ships were hit but these were barrier fields, not the ambush type mine fields that a submarine can create by sneaking into an enemy held area.
In Korea during the early 1950s, the Soviets provided North Korea with 3,000 mines, many of 1904 vintage. These were used to defend Wonson harbor. It took several weeks for UN forces to clear these, at a loss of a dozen ships hit. Half of these ships were destroyed.
During the Vietnam war over 300,000 naval mines were used, primarily in rivers. The vast majority were not built as mines but were aerial bombs equipped with magnetic sensors instead of fuzes. These bombs/mines used a small parachute to insure that no damage occurred on landing. In shallow water these makeshift weapons sat on the bottom and performed as well as mines. Haiphong Harbor was actually mined with 11,000 of these "destructors," as the US air force called them, and less than a hundred conventional mines. Haiphong Harbor was shut down completely for months, and it took years to clear out all the American mines. The "destructor" mine design was so successful that it is still in use, using more modern electronics, as the Mk 62 mine.
During the 1991 Gulf War the Iraqis laid over a thousand mines off the Iraqi and Kuwaiti coast. The predominantly US naval forces did not have sufficient mine sweeping resources to deal with this situation and had a helicopter carrier and cruiser hit and damaged while trying to clear the area. This effectively prevented any US amphibious operations, although the Marines were not going to be used for a landing anyway. It took over a month of mine clearing after the fighting ceased to eliminate all the mines. In the meantime, two U.S. warships were damaged by these mines. In 2003, the Iraqis again tried to use mines, but were hampered by prompt American, British, and Kuwaiti action.
In any future war naval mines will again surprise everyone with how effective they are. It is feared that terrorists might get their hands on some bottom mines, but so far, there do not appear to have been any attempts.