Do they have the "legs" to present a sustained threat in open water? Seems to me if they have to surface, even after a month, they become targets. And CERTAINLY they'll have to refuel, either from a surface ship or in port. Again, they become targets.
I can see how they would present a short-term threat to surface shipping...perhaps even warships. But over the longer term, nothing but targets.
Sure,they will have to surface & they can be sunk,just like any other ship,including N-boats which have to go up after about 90 days.The point is their potential for damage in the 2 or 3 weeks they are down in wartime.What's the point in sinking a 500 million dollar ship with 30 fellows on it after it has hit a SSN with 4 times the number of men & over thrice the cost,not mentioning surface ships.
Modern AIP technology is just evolving.This Swedish 'Sterling' AIP cannot go beyond 20 days-the new German fuel cell based systems can go upto 28 days & everyone is doing research to further that endurance.
The Germans have a new class of silent subs...based on fuel cell technology for generating electricity.....was on PBS couple of days ago.
One other note: How well can they detect us? US subs find it nearly impossible to detect another US sub.
The Persian Gulf area is tailormade for these boats or similar types. There is ample Iranian coastline to shelter and even fuel from, and with the worlds most important shipping lane within touching distance long legs are not needed.
In such an environment i wonder if some dozens of cheaper AIP boats may be more useful than 10 expensive Virginia class boats at something like $2billion each.
And remember, these Gotland class are old boats, the new German U212 class are better.