Declassified files on the Russian Navy's encounters with UFOs have suggested the objects are big fans of water.
A number of incidents were reported at Lake Baikal, the deepest lake in the world, including powerful lights and objects coming out from the water, Russia Today said.
In one case in 1982, military divers training at the lake said they spotted a group of humanoid creatures dressed in silver suits at a depth of 50 metres.They tried to catch the visitors but three of the seven men died in the process, while four others were severely injured in the incident, according to the records.
On another occasion, a nuclear submarine on a combat mission in the Pacific Ocean detected six unknown objects.
The captain of the vessel ordered the crew to bring it to the surface after failing to shake off the pursuers.The objects followed them up before flying away into the sky, the newly published files claimed.
Further mysterious events happened in the Bermuda Triangle area, including instruments on ships and submarines breaking down for no apparent reason.
Former navy officer Rear Admiral Yury Beketov said deliberate disruption from UFOs, which were detected "moving at incredible speed", could have been to blame.
He said: "It was like the objects defied the laws of physics. There's only one explanation: the creatures who built them far surpass us in development."
The records, which date back to Soviet times, were compiled by a special navy group tasked with collecting reports of unexplained incidents from submarines and military ships.