British media and politicians made much of the recent grounding of their new nuclear submarine HMS Astute. On October 22nd, the sub got snagged on a sand bank off Scotland for ten hours. This was during sea trials, and after it was freed, Astute collided with one of the tugs, causing more damage. Members of Parliament demanded to know, among other things, how often this sort of thing happened. They were told there had been seventeen collisions since 1988. One in that year, two in 1989, one in 1990, one in 1991, two in 1996, one in 1997, two in 2000, one in 2002, one in 2003, one in 2008 and two in 2009 and two, so far, this year. This made it clear that such collisions are not as rare as most people think.
This has to do with how the media deals with these events. For example, five years ago a U.S. SSN (nuclear attack sub) collided with an underwater mountain. The sub survived, but its sonar dome was smashed in, and one sailor died. This was big news, but most collisions are minor, and don't make it to the media. The navies involved like to keep it that way, if only to keep secret where, and when, their submarines operate. Most of the American collisions involve snagging fishing nets of large fishing vessels, or other lines (towing, anchor) hanging from surface ships. There was also lots of bumping into piers or buoys. Bumping into other ships or subs was also common. Most of the time, damage was minor, making it easier to keep such incidents quiet.
The Golden Age of submarine collisions was during the Cold War (1948-91). During the 1980s, the American force of over 130 nuclear subs suffered about six collisions a year, which comes out to about 4.5 percent of the boats colliding with something each year. Britain maintains a force of about a dozen boats, giving it a higher rate of 6.4 percent. The U.S. is believed to have reduced its collision rate since the end of the Cold War, but little official information has been given out.
The Russians are believed to have had an even higher rate of collisions, but they are even more secretive about it. Once Russia began building nuclear subs in the 1960s, and putting them to sea often and for long periods, there were lots of collisions, based on information that did get out. Most involved at least one Russian boat. The problem was that the Russians had pretty poor sonar, so they were the equivalent of half blind under water. From the 1970s on, the U.S. had increasingly superior sonar compared to the Russians. This led to more collisions involving Russian and U.S. boats. It also saw the invention, by the Russians, of the "Crazy Ivan" maneuver. This occurred when an American sub was stalking a Russian one (often an American SSN keeping tabs on a Russian SSBN). The U.S. boat would stay in the Russian subs "blind spot" (behind its propeller). But sometimes the Russians would suspect they were being stalked, or just wanted to make sure they were not, and would perform the "Crazy Ivan" maneuver, which involved upping speed and making a sharp turn. The U.S. sub would have to quickly get out of the way, or there would be, and sometimes was, a collision.
Most of the collisions during this period involved Russian subs bumping into other Russian subs, or inanimate objects (icebergs, oil rigs). Western boats had far fewer collisions because they had better trained and more experienced crews. This is especially true since the end of the Cold War, and the rapid shrinkage of the Russian sub fleet. The U.S. sub force also shrank, by about half, and underwater navigation became safer because of improved technology. But things still go bump in the deep, and most of these incidents will never be reported in the media.