A collision between two nuclear submarines took place at the beginning of February, raising fears of the release of deadly radioactive materials into the ocean, a British tabloid reported Monday. According to The Sun, the French Le Triomphant and the British Royal Navy's HMS Vanguard had around 250 sailors between them. Le Triomphant has a crew of 101. Vanguard has a crew of 140. Both subs are nuclear-powered and both carry nuclear missiles. An unnamed Royal Navy source was quoted as saying: "The potential consequences are unthinkable. It's very unlikely there would have been a nuclear explosionâ€¦ But a radioactive leak was a possibility. Worse, we could have lost the crew and warheads. That would have been a national disaster." The collision is believed to have taken place on February 3 or 4, in the mid-Atlantic. Both subs were submerged and on separate missions. Naval sources said the likelihood that both subs were in the same patch of sea was very low. Warships have sonar gear which locates submarines by sound waves, but also anti-sonar gear to make them "invisible" to enemy vessels. There is a possibility that anti-sonar technology made the subs invisible to each other. The British Ministry of Defense was quoted by the Sun as saying Sunday there had been no nuclear security breachÂ¸ but did not elaborate, adding that it did not comment on submarine operations. A naval source was quoted as saying "crashing a nuclear submarine is as serious as it gets."