Russia will reportedly soon tow its top-secret nuclear-powered Project 10831 Losharik spy submarine to a shipyard in northwestern Russian for extensive repairs. The boat suffered serious damage in a fire on July 1, 2019, that ultimately killed 14 submariners. Reports offering additional details about the accident have also begun to emerge, though the Kremlin has offered little in the way of official information about the incident, just as it has continued to be coy about exactly what happened during a recent explosion during a missile test that involved a nuclear power source in the same region. On Aug. 14, 2019, state-run media outlet TASS, citing an unnamed Russian defense industry source, reported that Losharik, also known by the hull number AS-31, would be heading in the fall to the Zvezdochka Ship Repair Center in the city of Severodvinsk in Russia's northwestern Arkhangelsk region. Zvezdochka is part of Russia's state-owned United Shipbuilding Corporation and has performed work on nuclear-powered submarines in the past. Representatives from Sevmash, the shipyard that built Losharik, as well as the Rubin design bureau, which crafted the submarine's specialized deep-diving design, which you can read more about here and here, will also be involved in the repair work, though there is no timeline yet for when the sub might return to service.

"This fall, Losharik will be towed for repairs to Zvezdochka," TASS's source said. They added that the first phase would involve pumping water out of the submarine, indicating that there had been flooding of one or more compartments, as well as a thorough inspection of the boat's titanium inner hulls to ensure its integrity had not gotten compromised in the accident. Lorsharik reportedly has a unique internal arrangement consisting of a number of spherical titanium alloy sections linked together that sit inside an outer hull that has a more traditional submarine shape. This is key to the submarine's deep-diving capabilities, which allow it to descend to depths of at least 3,300 feet, with some sources saying it can descend below 6,600 feet.

via Top Gear Russia A reported picture of Losharik running on the surface.

This is apparently also the source of the boat's name, which is a reference to a Soviet-era animated children's film about a circus animal shaped like a horse, but made from jugglers' balls strung together. "Losharik" is a portmanteau of the Russian words for horse, "loshad," and small ball, "sharik." After personnel at Zvezdochka get all the water out and conduct that initial inspection, then they can get to work on actually fixing the submarine's damaged internal components. TASS's source said the damage from the fire was "significant," but implied that the full extent of the situation remained largely unknown more than a month after the accident. "Preliminary estimates" had indicated that navigation equipment, life support systems, sonar components, and various other systems would need to be replaced entirely, they added. A second unnamed source had also told TASS that Sevmash would build new titanium hull parts, suggesting that the internal damage is far more significant than previously understood. This would align in many ways with a separate report from Russian newspaper Kommersant on July 23, 2019. Again, citing only anonymous sources with knowledge of the accident and its aftermath, it still offered one of the most complete accounts to date of what might have happened. The Main Directorate of Deep-Sea Research, Russia's main naval intelligence entity, also known by the Russian acronym GUGI, operates Losharik and its primary missions are investigating, manipulating, and recovering objects on the seabed, such hunting for items of intelligence value or tapping or cutting seabed cables. The small submarine is also designed to ride underneath a larger submarine mothership to get closer to the target area. GUGI has a number of motherships converted from ballistic missile and cruise missile submarines. Losharik was reportedly attached to the modified Project 667BDRM Delfin-class ballistic missile submarine BS-64 Podmoskovye following a training exercise in the Russian Navy's Northern Fleet's training ground in Motovsky Bay in the Barents Sea when the fire broke out on July 1. The fire, which started in Losharik's battery compartment, did not appear to be particularly serious initially, according to Kommersant's sources. You can read about why fires onboard submarines can quickly and easily become very serious in this previous War Zone story.

TASS BS-64 Podmoskovye at the Russian Navy base in Severomorsk after the accident.

Still, 10 members of the spy submarine's crew, reportedly remained on board to fight the fire, using PDU-3 portable breathing devices, which have enough oxygen to allow the user to breathe for up to 20 minutes. Russian Navy rules also stipulate that a submarine's crew remain in place to deal with any fire, unless specifically ordered to evacuate, on penalty of criminal charges, Kommersant's sources said. Kommersant's sources could not say for sure what happened next, since all 10 of these individuals subsequently died and the investigation to determine the causes of the accident and what exactly transpired remains ongoing. These submariners reportedly fought the fire for more 40 minutes, exchanging their first PDU-3s for additional fresh ones from the stocks onboard and then using a fixed emergency breathing apparatus to continue their work.

Zelinsky Group A newer PDU-4T "escape hood" emergency breathing device. This is similar in general concept to the PDU-3s that the crew of Losharik reportedly wore while fighting the fire.