Collision of two submarines on 01 March, 1975 in the Kola Gulf.
A Soviet Project 667A (Yankee I) Nuclear Ballistic Missile Submarine (SSBN) was returning to base after patrol. The boat should have met the duty escort ship, which would have led her during her entrance into the Kola Gulf. The escort MPK (Small Submarine Ship) got underway late and failed to escort the returning submarine. At the same time, a Project 641 (Foxtrot) diesel submarine (SS) was putting to sea, heading out to the range for training. The commander of the SSBN didn’t properly evaluate the situation and took the contact he had to be the escort ship. Visibility was 30-40 cables, sea state was two, wind was 195 at five meters/second (appx 10 kts). The SS was sighted at 0626 and no precautions were taken on the part of the SSBN since it wasn’t identified at the time. The SS exited the Kola Gulf at 0600 two cables to the port of the channel centerline because of a delay in making the turn. The commander and the navigator of the SS knew about this, but despite this turned off the radar and secured the maneuvering watch in combat. The CO of the SS was informed about the possibility of a meeting with a returning SSBN, but no precautionary measures were taken and she continued to proceed at 9.5 knots. The SSBNs running lights were sighted at a range of 30 cables and the boats continued to close dangerously. The CO of the SSBN continued to count on the fact that the escort MPK was dead ahead, which should have been at a position 10 cables ahead. Because of an incorrect evaluation of the situation, he acted in an indecisive manner and maneuvered dangerously. The Foxtrot was detected by radar at 0615 and in 11 minutes was spotted visually. At 0628 a report from combat came about a dangerous approach and the captain of the Yankee I slowed from ten to seven knots. Within five minutes both boats closed to a distance of four to five cables and the commander of the Foxtrot gave the command, “Hard to port, course 070!” Simultaneously, the SSBN put its rudder “hard to starboard” and in a minute threw the engines full astern. At 0634 the Foxtrot began its left turn and thirty seconds later, stopped its engines. At 0635 the Foxtrot was in a left turn and inertia and a 7-8 knot headway carried it into the bow of the Yankee. The blow came to the starboard side of the SSBN at a 35-40 degree angle. Both submarines suffered damage to the outer hull and the hydroacoustic station on the Foxtrot was completely destroyed.
(Translation by the Russian Submarine Blog. Source: www.shipandship.chat.ru)