Norway is modifying its Tromso naval base to accommodate American nuclear submarines. These modifications include a well-guarded berthing area for the largest American SSN (nuclear attack sub) the USS Carter, a modified (for intelligence work) Seawolf class SSN that underwent nearly a billion dollars’ worth of modifications and upgrades that turned it into a 12,100-ton boat that is 138 meters (453 feet) long and extends 10.9 meters (35.8 feet) underwater. Most American SSNs displace 7,900 tons and are 115 meters (377 feet) long. The largest American subs are the Ohio class SSBNs (nuclear powered ballistic missile carrying) boats which displace 18,700 tons, are 170 meters (570 feet) long and extend 10.8 meters (35.5 feet) underwater.
The Carter has a crew of 141, and is 30 meters (100 feet) longer than the other two Seawolfs to accommodate a 2,500-ton middle section containing a MMP (Multi-Mission Platform) that can deploy divers and ROVs (Remotely Operated Vehicles) and other special equipment for intelligence work. The Carter was the last of the Seawolfs built and entered service in 2004. The Carter was intended for undersea or amphibious intelligence work. In 2010 the Carter was used to assist South Korea in the aftermath of a recent attacks by North Korea, which included a North Korean mini-sub torpedoing and sinking a South Korean corvette.
American SSNs often call at American naval bases overseas to take on supplies or for minor repairs. SSBNs stay under water for their three-month tours at sea and then return to their homeport in the United States to take on supplies and a new crew before going out again. The Carter retains its weapons which include eight torpedo tubes plus up to 40 torpedoes or cruise missiles and up to a hundred naval mines. All three Seawolfs are the quietest nuclear subs in American service, and probably the world. The Seawolfs, and especially the Carter, have already been operating near Norway in the northern waters that contain the largest Russian naval bases and most of its warships. The offshore waters are regularly used for Russian and NATO naval exercises.
The smaller Olavsvern naval base is outside the port city of Tromso, 375 kilometers west of the Russian border and the Kola Peninsula where many of the Russian naval facilities are located. Olavsvern, which includes a tunnel complex accessible by seagoing ships, was shut down in 2009 but soon Norway found that it still needed a naval base that far north. By 2014 Norway was regularly allowing NATO warships to use part of the civilian port of Tromso and that led to the 2016 decision to reactivate Olavsvern as a naval base, especially for NATO and Norwegian submarines.
In 2012 Norway sold the Olavsvern underground submarine bases for $17.5 million. Located outside the city of Tromso, next to highway E8, the former Olavsvern Naval Base is basically a water level tunnel dug into a mountain at the mouth of a fjord, one of the many deep-water channels that give the Norwegian coastline that heavily indented look. The tunnel can dock small warships or a submarine and has 25,000 square meters (269,000 square feet) of underground space. There are several tunnels down there, most of them dry. The above ground structures contain 13,500 square meters (145,000 square feet) of space. Built in the 1970s at a cost of several hundred million dollars, its industrial grade space hasn't been used by anyone since the military moved out in 2002. In 2015 the Norwegian military obtained a long-term lease for the Olavsvern underground facility and several other bases along the coast that had also been sold off, but were now deemed needed once more for Norwegian and other NATO naval forces. The Olavsvern underground dock is too small to handle the larger nuclear submarines, especially one of the three American Seawolf, but is a very safe place to store supplies, especially spare parts, for the Seawolf and other naval ships that want to use Olavsvern rather than returning to more distant naval bases equipped for that task.