This is becoming a habit

Another US submarine had a prang in the Strait of Hormuz. I believe this puts us at number three.

A nuclear-powered submarine, the USS Hartford, and amphibious transporter the USS New Orleans collided early on Friday, the US Navy Fifth Fleet said.

The incident is being investigated and damage to both ships is being evaluated, a navy statement said.

The New Orleans' fuel tank was ruptured in the crash, causing a spill of 25,000 gallons (90,000 litres) of diesel.

No injuries were reported aboard the New Orleans, according to the statement from the Fifth Fleet, which is based in Bahrain.

The US military said there was some damage to the USS Hartford's sail, the tower structure on the top of the submarine.

Which would suggest the Hartford was dived.

In January 2007, USS Newport News had a top to bottom collision with a merchant ship in the same place. In September 2005 USS Philadelphia had a surface collison with a merchant ship making the fact that Philadelphia was a submarine somewhat irrelevant since she was on the surface.

But, once again, it seems like there is a lack understanding for the conditions in the Strait of Hormuz.

It's simply not an easy place to maneuver. It's tight. Sometimes it's busy. And for a submarine it's more than a little bit of challenge.

The bottom topography of the Strait is less than favourable and there are two factors which, if ignored, can wreak havoc with a passage plan:

1. There is a weird counter-flow current through the Strait. If you're, say, deep (that's a relative term considering the position of the bottom), and you come up to periscope depth you can be in for a nasty surprize. If at depth you were making perhaps 12 knots over the ground and then surfaced to periscope depth you would find yourself going much faster as the current changed direction. If you were unaware of this it might make for a early arrival under a surface contact which you had plotted much farther away. Not a good thing.

2. Over the years there has been reported a significant"salinty lense" in the Strait of Hormuz. It's temporary but any submarine which encountered it would experience an unanticipated and unwelcome boost in buoyancy. That can ruin your whole day.

In any case, Hartford was obviously rolled onto her side with 15 people injured.