Gotland.

This is coolbert:

Within the context of the recent Swedish submarine scare and hysteria, and the recent blog post the topic of which was the American Arctic Submarine Laboratory, it might be well worth it to consider the Swedish air-independent-propulsion capable Gotland class submarine.

"Sweden Has A Sub That's So Deadly The US Navy Hired It To Play Bad Guy"

"We have been glued all week to the sub saga off the coast of Sweden, where six days in Swedish forces have only now called off their search for an elusive sub hiding in the waters off Stockholm. Yet what nobody has mentioned is just how deadly and capable Sweden's own subs are, and there are few better weapons for catching a sub than another sub."

"Sweden's submarine force is relatively tiny, just five boats make up the entire inventory, but those five vessels are extremely stealthy and lethal, especially their three Gotland Class diesel-electric submarines . . . Gotland Class was the first operational Air Independent Propulsion (AIP) submarines in the world, which gave them the previously unprecedented operational ability (for non-nuclear submarines at least) to stay submerged for weeks at a time."

Diesel/electric boats I might assume able to operate under the pack ice of the Arctic and do so for prolonged periods of time. What was once only within the purview of the nuclear powered submarine is now possible for those nations having AIP boats.

coolbert.