Trident II D5
The U.S. Navy has conducted test-firing of Trident II D5. Picture: The Ohio-class ballistic-missile submarine USS Tennessee (SSBN 734) departs Naval Submarine Base Kings Bay to conduct routine operations, in Kings Bay, Georgia, July 22, 2014.Reuters

Only seven countries in the world have nuclear-powered ballistic missile submarines or Ship Submersible, Ballistic and Nuclear (SSBN) and they represent one of the most powerful deterrents for all-out war in many parts of the world.

India has two such submarines that are capable of laying low in stealth and firing as a means of retaliation in case an adversary should attack the homeland.

SSBNs are known to be difficult to track and find in the open sea and are likely to survive a first strike, lay in waiting and then respond with deadly nuclear retaliation, notes a report by Popular Mechanics.

The US Navy controls the largest fleet of nuclear submarines in the world - they have 14 Ohio-class submarines, each displacing 18,800 tons.

Second is Russia with the most variety of vessels, notes the report. Russia has four 24,000-ton Borei I class SSBNs, six 18,200-ton Delta IV class submarines, one recently overhauled Delta III class SSBN and the last still operational Typhoon class submarine called the Dmitriy Donskoy, the largest submarine class ever built. That is a total of 12 nuclear submarines for Moscow.

The Typhoon class submarines are so large, notes the report, that they displace more than twice as much as the American Ohio class vessels at 48,000 tons.

As far as China is concerned, the country is known to have at least four nuclear submarines, with some estimates saying six SSBNs of the Jin class, one submarine in the Xia class and a few other conventional boats that are highly capable. China now has the largest conventional diesel-electric sub in the world.

The United Kingdom and France command four SSBNs each. The UK's SSBNs are Vanguard class vessels, displacing about 15,900 tons. The French Navy operates the Triomphant class submarine, displacing 14,300 tons each. Both these vessels are the largest ever built subs by both countries.

New entrants to the SSBN club

India and North Korea are the newest entrants to this elite club.

The Indian Navy currently has one Arihant class submarine that was designed and built in the country. India is the first country to design and build its own SSBN; it is also first nation outside the five permanent members of the UN security council to do so.

The submarines are capable of carrying and firing ballistic missiles - 12 K-15 missiles in four launch tubes. The missiles can be armed with one warhead and an effective range of about 750 km or four K-4 missiles with a range of nearly 3,500 kilometers. The Arihant displaces about 8,000 tons. One more submarine much larger than the current vessel is set to be deployed in the near future.

Meanwhile, North Korea has two SSBNs that have so far been identified - the 1,700-ton Sinpo class (also called the Gorae) SSB. This is the smallest nuclear-capable submarine in the world, notes the report. Displacing a mere 1,700 tons, it is the DPRK's first ever submarine. Recently, one more submarine was detected by US intelligence designated Sinpo-C. This one was found to be slightly larger and is likely larger than 2,000 tons.