"A Royal Navy nuclear submarine was involved in a collision in the middle of the Atlantic, it was reported.
The crash between HMS Vanguard and French submarine Le Triomphant, which was also carrying nuclear warheads, is believed to have occurred on February 3 or 4, The Sun claimed."
A nuclear submarine seems to be about 140 meters with a radius of 12. So that's a volume of about 63360 cubic meters.
The Atlantic ocean is 354,700,000 cubic kilometers. There are 1 000 000 000 cubic metres is a cubic kilometer. Of course subs can only dive to about 400 metres. So say they stay in the top 300 meters then the volume might be more like 106.4 million km squared * 300 meters=30 million cubic km. More likely they avoid the top 20 meters where ships might hit them, so their range is estimated to be 20-2320 meters deep.
This is assuming a submarine is a cylinder which it isn't.
How many nuclear submarines are there? There seems to be about 50 in the world. Navies will keep their own submarines separate. But that still means there are in the Atlantic maybe 25 submarines that the French or UK subs could run into. This does reduce the number of subs the Russians Or Americans can hit significantly though. They have a top speed of about 40 km per hour. So I assume they are wandering around at 20kph. So assuming all the worlds submarines are in the Atlantic ocean at the same time how often would you expect one to hit another if they were traveling round at random?