There are two versions of the story. The first alleges a collision, but with whom is not mentioned:
An SSBN was returning to base from combat preparations at the range. The boat was at a depth of 50 metes and was proceeding on a course of 180, 9.5 knots. The commander of the Soviet boat formally checked on the absence of a trailer and at 1930 ordered a sound level measurement. At 1951, the "K-211" experienced three unexpected shocks lasting 10 seconds. The commander of the Soviet boat decided to proceed to periscope depth, but received a report from sonar about propeller sounds off the port side bearing 127. Sonar classified the contact as an SSN. At 1958, "K-211" maneuvered to starboard of the supposed contact and within two minutes contact with the foreign submarine was lost. "K-211" surfaced at 2011 but didn't detect anything visually or on radar. An inspection of the hull back at base showed insignificant damage to the rubberized covering of the hull of the Soviet SSBN from a glancing blow.
The second version of the story names a villain (the United States, naturally) and reveals that the damage was much more extensive than minor damage to the rubberized coating:
A collision between the nuclear submarine "K-211" and an American Sturgeon SSN occured in a training area near the Kola Gulf in 1981. An American submarine hit the stern of the newest SSBN "K-211", which had just joined the Northern Fleet and was testing elements of combat readiness, with its sail. The American boat didn't surface in the area of the collision. But a few days later an American SSN appeared at the British Naval Base at Holy Loch with severe damage to the sail. Our boat surfaced and returned to base under its own power. There it awaited a commission, consisting of navy specialists, production specialists, scientists and contractors.
The commission, having modeled the maneuvering situation of the two boats and having inspected the damaged area, determined that the American bost was following our boat, remaining in her acoustic shadow. As soon as our boat changed course, the American boat lost contact and collided with its sail into the stern of the Soviet boat. She was put into the dock and there an inspection revealed punctures in two main stern ballast tanks and damaged blades on the starboard screw and horizontal stabilizer. Bolts and rivets were found in the damaged ballast tanks and pieces of metal and plates from the American boat's sail. Additionally, the commision was able to establish that the collision was with an American "Sturgeon" boat which was confirmed to have showed up at Holy Loch with a damaged sail.
As far as it is known, "K-211" continues service in the Pacific Fleet in the 16th Submarine Squadron based at Rybachyy, Petropavlovsk.