According to the British Broadcasting Corporation (BBC), a British and a French nuclear submarine collided in the middle of the Atlantic Ocean earlier this month.

HMS Vanguard and Le Triomphant are both part of a four-vessel nuclear submarine fleet in their respective countries. At the time of the incident, both were carrying nuclear missiles.
Although both vessels were damaged, none of the collective 240 crew members were reported injured. HMS Vanguard had to be towed back to its base at Faslane on the Firth of Clyde (Scotland), while Le Triomphant came back by its own means to its base at L'Ile Longue near Brest in north-west France.

The United Kingdom and France both assured that nuclear security had not been breached during the collision. However, neither of the two vessels picked up the others sonar signals.

Now, excuse me if I'm wrong, but the Atlantic Ocean seems to be quite a large body of water, given that it's the second largest ocean in the world. What are the chances of two nuclear submarines both diving at the same depth at the same spot in a massively vast ocean??

Furthermore: Shouldn't the sonar system on every ship, let alone a nuclear submarine, work constantly and without fail? Luckily, both vessels were diving at low speeds, so the impact of the collision did not trigger the weapons to detonate. If they had gone any faster, a nuclear catastrophe might have been unavoidable, and would have released vast amounts of radiation, left the ocean polluted and nuclear warheads scattered across the oceanbed.

I guess, the world can count itself lucky that the United Kingdom and France are not nations at war with each other. This incident, accident or not, might have easily triggered a nuclear war.