To properly describe how and why the USSR dissolved is pretty lengthy. A number of factors including growing nationalism from individual states, a stagnant economy, the easing of tensions between the USSR and the U.S, Perestroika and glasnost revelations and of course the Chernobyl accident all played significant parts in the demise of the USSR.
Today Back Then
In the early hours of January 1st 1915 , the HMS Formidable was sank by a German U-Boat, not far off the coast of Devon. Although there was rumour of possible nearby enemy vessels, bad weather at the time made the commanding officers think that a submarine attack would be unlikely.
Follow this link to wiki to find out more about the story.