[Lonesome in Massachussets]

I would assume the submarine would have been at a depth of several hundred feet.

The South China Sea is shallow and not an ideal submarine operating area. They were obviously there to sniff around at the Chinese Navy, and the Chinese may have deliberately interferred with their mission. It happens.

[Lower Deck]

The South China Sea is shallow and not an ideal submarine operating area.

Depends on where they were at. Much of the South China Sea is thousands of feet deep. Other areas, like the Taiwan Straight, are only a few hundred feet deep.

They were obviously there to sniff around at the Chinese Navy, and the Chinese may have deliberately interferred with their mission. It happens.

Perhaps. But if they were close inshore that makes a collision with an uncharted seamount an even more likely explanation.