Submarine environment more treacherous

BACKGROUND

Molten Eagle - 27 June 2013...
"...[C]onsider the updated threat potential to a US submarine suddenly beset by a swarm of dozens of  autonomous underwater vehicles [UAVs]  configured to suddenly activate and mimic submerged packs of hostile subs. Would the sudden distraction allow a real enemy sub to penetrate a protected patrol zone, torpedo the US sub?   How long would it take to verify the actual threat? The hostile force could easily increase complexity (add confusion) by mimicking several types and nationalities simultaneously. Some swarm units might also be configured as high tech torpedoes."

FLASH FORWARD

NEWPORT, R.I., 15 April 2016...  Navy orders underwater drones that can mimic the behavior of quiet enemy diesel submarines.

 U.S. Navy anti-submarine warfare (ASW) experts needed target underwater drones that mimic the acoustic and non-acoustic signatures of advanced nuclear- and diesel-powered submarines. 

Submarines are always silent and strange.