[NorseViking]

There was the USN drill in the area in June. Before the incident there was a USN ship and launched a helicopter which flew exactly where the explosions took place.

[agere_contra]

There was the USN drill in the area in June.

Correct - that was BALTOPS22

That link is a very interesting read.

[laplata]

And the USN carries underwater drones on ships like the USS Kearsarge.