https://www.popularmechanics.com/military/navy-ships/a14783891/someone-left-a-hatch-open-and-crippled-indias-dollar29-billion-submarine/

Someone Left a Hatch Open and Crippled India’s $2.9 Billion Submarine

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India’s first ballistic missile submarine was out of commission for ten months after someone neglected to properly close a hatch. The nuclear-powered submarine INS Arihant was flooded with saltwater, necessitating nearly a year’s worth of repairs. The submarine is designed to function as a floating arsenal of nuclear weapons, guaranteeing a retaliatory strike in case of surprise attack.

The incident was first reported by The Hindu. According to an Indian Navy source, a hatch was left open on the rear left side of the ship, allowing seawater to rush into the propulsion area while the Arihant was in harbor. Arihant was out of action for ten months as water was pumped out and pipes were cut out and replaced. Indian authorities likely felt that pipes exposed to corrosive seawater couldn't be trusted again, particularly pipes that carry pressurized water coolant to and from the ship’s 83 megawatt nuclear reactor. Failing pipes could not only endanger the ship’s crew but the entire submarine... and her nuclear weapons.

India’s first ballistic missile submarine is the result of a $2.9 billion submarine technology program. Construction on Arihant began in 2009, and the ship was commissioned into the Indian Navy seven years later in October 2016. The modified Russian Akula-1 class nuclear attack submarine was lengthened to accommodate twelve K-15 short-range nuclear missiles or four K-4 intermediate range nuclear missiles. K-15 missiles, with their 434-mile range, primarily target Pakistan, while K-4 missiles, with their 2,174-mile range can reach all of Pakistan and as far as the capital of India’s other neighborhood rival, Beijing. A second missile submarine, INS Arighant, was launched in December, and at least three submarines are planned.

How in the world could a $2.9 billion submarine be sidelined by a simple mistake? Not leaving hatches open that could potentially sink a ship, particularly a submarine, is basic common sense. Why were the propulsion section and nuclear reactor on the 364-foot long submarine unattended so the flooding went unnoticed as long as it did? As the star of the Indian Navy, Arihant should have attracted the best submariners India had to offer, which makes this accident all the more baffling.

(http://www.autoadmit.com/thread.php?thread_id=5759567&forum_id=2Elisa#49164577)

2017 accident

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In January 2018 it was alleged that an aft hatch on the submarine was left open by mistake while the Arihant was docked in 2017, leading to saltwater flooding the propulsion compartment, rendering the submarine inoperative for ten months while corroding pipes were replaced.[46][47][48][49] These allegations were dismissed by some sources due to the submarine being based on a double hull design[50] as well as claims that it does not have a hatch to the propulsion compartment. However, the Indian Ministry for Defence refused to deny the allegations, claiming it would be a breach of national security to speak on the matter.[51][

(http://www.autoadmit.com/thread.php?thread_id=5759567&forum_id=2Elisa#49164697)