Read the article. The French were well aware that they had git something. They just didn't know what. The only way that you would know is if you heard it before or after the crash. As its sonar dome was damaged, that leaves only the before part.
A better question would perhaps be to ask how the British knew what they hit, but didn't avoid it.
It was the french who did the hitting, not the british.
Based on the damage to the bow/ sonar dome and array of the Frech sub, and the lesser hull damage to the Brits, one could reasonably infer the Brits were ‘crossing the T’ of the French boat, from a maneuvering standpoint.
“Acoustic contact close aboard contact, Captain. Range 100m on starboard quarter!”
“Helm, all ahead full. Left full rudder. 20 degrees up on the planes!” Except none of that apparently happened???
Two deaf or inattentive boats.
OK, so since the French did not hear the Brits, one could presume the Brits did not sound a collision alarm, did not ping, did not try to warn away ... i.e., the Brits were unaware of the French boat until it motored away under it own power. Then the Brits figured out they had been in a collision (a) with another sub, and (b) it was the Frenchies. Merde! Or did they?
And for the French. They never figured out they hit a sub. So the Brits never did anything to provide an acoustic signature ... even if the French could ‘hear’ anything. i.e., the Brits continued ‘silent running’ while they performed their damage assessment.
Or maybe everybody knew what actually happened in a game of chicken, and no one wanted to own up to it.
The obvious question is was this really a 1 in a million encounter in the cubic miles of the ocean, or were these two boats messing with each other? Makes no sense for two boomers to do it ...
just pondering