This link is to an article describing the impressive characteristics of Sweden’s Gottland class of super stealthy submarines. In brief,  the the subs in this class are undetectable.
This is an important article for those of us concerned about the naval aspects of defense policy.

http://foxtrotalpha.jalopnik.com/sweden-has-a-sub-thats-so-deadly-the-us-navy-hired-it-t-1649695984