On 1 July 2019, a fire broke out on the vessel while it was taking underwater measurements of the sea floor in Russian territorial waters.

[9][10][11][12][13][1][14] The pressure hull of the submarine is believed to be formed from up to seven interconnected titanium spherical elements; this limits space for living quarters and equipment, but grants increased structural strength.

It is known to have operated at about 2,000–2,500 metres (6,600–8,200 ft) depth in the Arctic Ocean in 2012[3] and is capable of being carried by a modified Delta III-class submarine.

[18] The vessel was referred to in a United States Northern Command briefing as a "dark target" whose activities should be tracked.

[19][20] The Project 09852 modified Oscar-class submarine Belgorod, was specially refitted beginning in 2012 in order to transport Losharik, in support of GUGI operations.

[21][a] A fire broke out on the vessel on 1 July 2019 while it was taking underwater measurements of the sea floor in Russian territorial waters.

[28] Losharik was later towed to the Russian Northern Fleet base at Severomorsk where five survivors were hospitalised with smoke poisoning and concussions.

[29] Initial reports indicated that Losharik was not attached to its mother submarine when a fire broke out in its battery compartment and that only 5 crewmembers were on watch at the time of the accident with the rest allegedly asleep, as a result only the 5 crewmembers who were on watch managed to don the portable breathing kits in time.

[33] Crewmembers fought the fire for over 40 minutes and then requested permission to evacuate to the mother submarine when the oxygen supply in their portable breathing devices ran out.

[39][28] On 2 July, Shoygu reported on the fire to Putin, the Supreme Commander-in-Chief of the Russian Armed Forces, at a meeting in the Kremlin.

[40] Some journalists speculated that the men who died had sacrificed themselves to save the vessel by sealing themselves into the compartment where the fire broke out.

[24] On 7 July 2019 at the sailors' funeral, Captain Sergei Pavlov, an aide to the Russian Navy head, proclaimed the crew "prevented a planetary catastrophe".