Very recently there were two collisions at sea involving submerged nuclear submarines. Strategic missile "boomer" SSBN subs from the UK and France collided while both were submerged out on patrol, and just the other day a submerged U.S. Navy fast attack SSN, USS HARTFORD, collided with a big U.S. Navy amphibious transport dock ship, USS NEW ORLEANS, in the Strait of Hormuz. Injuries were light-to-none, and all ships continued into port under their own power for damage assessment and repair. As naval spokespeople hastened to assure world media and the public, the nuclear reactors and nuclear weapons were never endangered.
Which is good, but even so, what gives?
While submarine operations are top secret by necessity, it's possible to offer educated conjecture based on public information as to possible explanations for both incidents. Submarines are notorious enough as being, and as facing, collision hazards when running on the surface; in late 2005, near the same Hormuz Strait, the fast-attack USS PHILADELPHIA while surfaced was run down and moderately damaged by a Turkish cargo ship. When submerged and shallow, submariners do, or at least ought to, take excruciating precautions against hitting something or being hit themselves -- the tragic surfacing of USS GREENVILLE right through the hull of a Japanese fishing ship off Hawaii in 2001 served as a terrible reminder of that.
But what brought two naval vessels, with at least one of them a submerged sub, close enough together to begin with -- to have such major nautical fenderbenders -- could have been the realistic training exercises that submariners must constantly undergo to be thoroughly prepared for their dangerous and demanding jobs.
Scenario for the UK/France collision: The two boomers may have been practicing sub-on-sub combat maneuvers, including the classic close-trail so well dramatized in "Hunt for Red October." Would two boomers ever fight in a real life war situation? Oh yes! It's public info that SSBN crews train hard so that, if they ever do have to launch their missiles, they and their sub can then stay immediately useful and relevant by switching over to the attack as an ersatz SSN, to go on the hunt for enemy SSBNs. (Their extreme quiet, powerful passive sonars, and heavyweight anti-sub torpedoes make them decent platforms in that role.)
In addition, it's public info that to save money and maximize utility of all navy assets, SSBNs while transiting to and from their patrol areas will sometimes serve as "training targets" for anti-submarine forces. Either of these situations could account for why the Royal Navy and French SSBNs were so close together to begin with that they collided while submerged. Statistically speaking this seems more likely to explain it, rather than a totally random encounter against astronomical odds under the high seas.
Scenario for the Hartford collision: The Strait of Hormuz is a narrow and crowded waterway of vital strategic and geopolitical importance, because it's a crucial choke point in the shipping of petroleum products from the Middle East. It's possible that the Hartford was operating in concert with other U.S. Navy forces to get realistic practice in how to protect and dominate the Strait -- what the Pentagon calls Sea Access and Sea Denial, two essential parts of maritime security operations.
So, think back to old WWII movies such as "Destination Tokyo." Another classic submarine tactical maneuver is to sneak through a strait by hiding under a big surface ship, and this tactic needn't be confined to diesel subs. It could be that Hartford and the amphib were practicing just such an evolution when the collision occurred. It could be that part of the exercise was for Hartford to do this undetected, with the amphib unawares. (A very similar collision in the same place in early 2007, between the L.A.-class USS NEWPORT NEWS and a Japanese oil tanker, was blamed in part on the treacherous suction forces that are caused during such a maneuver.)
Hartford might even have been tasked with sanitizing New Orleans against an actual or hypothetical Iranian diesel boat. Though such truths may never be revealed, something like this, and not a crash between two mutually sonar-blind-sided warships, might explain why Hartford while running submerged and shallow was so close to a big and noisy surface vessel to begin with, as to collide with her.
-- Joe Buff