The USS Jacksonville, a large nuclear submarine, has broken its periscope after colliding with a vessel which escaped unscathed. This is the latest collision to involve a US vessel in the busy and tense oil chokepoint of the Strait of Hormuz.

The American sub was performing a routine pre-dawn patrol when seamen heard a “thump”, according to a Navy source who spoke to several news agencies. The crew tried to ascertain the damage by looking into its periscope, only to realize it was no longer working. The other periscope on the submarine revealed that the first one had been“sheared off”.

It appears the ‘fishing trawler’ that collided with the 7,000-tonne submarine was not only undamaged, but barely noticed the accident.

“The vessel continued on a consistent course and speed, offering no indication of distress or acknowledgement of a collision,” says an official statement published on the US Navy website.

Authorities insist that USS Jacksonville is in no immediate danger.

“The reactor remains in a safe condition, there was no damage to the propulsion plant systems and there is no concern regarding watertight integrity,” they said.

The cost of repairing the damaged periscope are as yet unclear, but the discontinued Los Angeles-class submarines, to which USS Jacksonville belongs, would cost over $1 billion to build in today’s money (the sub was launched in 1978).

USS Jacksonville has now returned to Bahrain, where its damage will be assessed.

The Strait of Hormuz, by far the world’s busiest oil choke point and less than 40km across at its narrowest, has been a scene of several collisions since tension has risen between Iran and the US over the past two years.

The latest spiral of tension in the waterway, which is controlled by Iran on the north side, and US allies Oman and the United Arab Emirates on south, started with the gradual imposition of sanctions on the export of Iranian oil to most Western countries over the last two years.

In response, Iran has repeatedly threatened to close the strait, which transits a third of the world’s sea-borne oil, through ‘asymmetrical’ measures such as laying extensive minefields.

To counter the threat, the US and its allies have deployed what UK media has reported is the biggest concentrated naval force since World War II.

In the crowded passageway, with distrustful captains from dozens of nations operating at cross-purposes, collisions are inevitable.

Most notably, in August last year a Japanese oil tanker left a 3-meter-wide hole in the side of Navy destroyer USS Porter.

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