UPDATE :
The US has carried out a submarine torpedo strike that sank an Iranian warship off the south coast of Sri Lanka, according to the US secretary of defence.
Pete Hegseth confirmed that the US was behind the deadly strike on an Iranian frigate that was travelling close to the Sri Lankan coast.
“An American submarine sunk an Iranian warship that thought it was safe in international waters,” Hegseth said. “Instead, it was sunk by a torpedo.”
US submarine sank Iranian warship off Sri Lanka’s coast, Hegseth says


Its simply that the US hasn’t needed to. There have been three ships sunk by torpedoes from a sub since 1945.
Improvements in communication security and aerial capabilities mean its more advantageous to preserve the invisibility of the submarine and use it to identify and track targets, and for aerial and surface combatants to engage.
If you actually mean they haven’t been used — they have. They’re very powerful tools for intelligence gathering.
That was my point.
You can bet your ass that Iran (& any others operating in the region) will be sharing those sensor logs with China to lessen the invisibility of US submarines.
What sensor logs? The first time that ship was aware something was up was when the stern blew off.
Pretty sure there are other things in the Indian Ocean with sensors, and even the ship that was hit likely has sensor readings that in retrospect can make spotting US subs easier.
Acoustic buoys? Your expectations may be a bit high. It took days to find the Titan submersible when they had acoustic readings, they knew where it was aiming to go, it wasn’t moving, and it wasn’t actively hiding. The ocean is rather vast.
China & Russia have subs too and when Titan went smush nobody was going to give away that they heard it, but it’s likely that if any military had cared it would have been found much sooner.
Yeah, you can tell from the video that crew were mustering on deck. They had 0 knowledge they were under attack.