The A.P. reports:

Two U.S. Navy vessels—a nuclear-powered submarine and an amphibious ship—collided before dawn Friday in the mouth of the Persian Gulf, one of the world's most important sea passages for oil supplies.

There was no damage to the sub's nuclear propulsion system and no disruption to shipping in the strategic Strait of Hormuz, through which a fifth of the world's oil passes, said Navy spokesman Lt. Nate Christensen, with the Bahrain-based 5th Fleet.

Still, the unusual collision between members of the same navy sparked a sudden rise in oil prices—which had been declining on the day—even though the strait remained open.  [...]

The incident occurred around 1:00 a.m. local time Friday (5 p.m. EDT, Thursday), when the USS Hartford, a submarine, and the USS New Orleans, an amphibious ship, collided into each other in the narrow Strait of Hormuz, the 5th Fleet said in a statement. 

This is the second collision involving nuclear submarines in as many months. In February, British and French subs carrying nuclear warheads bumped into each other in the North Atlantic. Here's what Ian Bremmer wrote about that crash over at The Call:

First, this is not as unlikely an accident as you might think. These subs tend to pass through regions of the Atlantic where the Gulf Stream is strongest and they're, therefore, hardest to detect.

Second, both countries are extremely secretive about the positions of their submarines. On board, only the captain and senior officers generally know with much precision where they are. France will finally rejoin NATO's military structures this April, but that's unlikely to make them any more forthcoming about the nuclear submarine force.

Finally, stealth sonar technology works. Neither of the submarines would have detected the other--even at close quarters. These are the main reasons why this collision was merely really, really, really unlikely rather than virtually impossible.

Sounds reasonable. But I would imagine that it's even more unlikely for a submarine to crash into a ship from its own navy on the surface. The New Orleans doesn't look all that stealthy.

http://passport.foreignpolicy.com/jkeating