[spetznaz]

I wonder how quiet they are?

The new D-E subs (especially the ones with AIP systems) are basically mines in the sea .....super-quiet and potentially lethal (especially if they lay low in littoral waters and wait for targets). They are actually quieter than nuclear subs (because a nuke sub needs to cool its reactor, hence it has a certain level of ambient noise).

In adequately trained hands, and within a certain envelop (eg within littoral waters), a modern D-E sub with AIP is an extremely viable threat for any submarine.

[clee1]

Damn! That is just what I was afraid of.

OK France... When Germany comes calling (again), DON'T bother asking the USA for help.

[CasearianDaoist]

They also have limited blue water reach. We need to get on top of this technology too but the nuke mafia in the Sub force has always obstructed any attempt to build this smaller class of subs. One day one of them will sink a carrier. We can barely track them now, wait a few years.