Mick Hartley

To much fanfare, the North Koreans have launched their new fearsome nuclear attack submarine:

Photo: KCNA/Reuters]

North Korea has unveiled what it claims is a "tactical nuclear attack submarine." State media last Friday said the North completed the sub in Sinpo, South Hamgyong Province over the last four years.

North Korean leader Kim Jong-un also vowed to develop a nuclear-powered submarine that can stay underwater "for several months" without resurfacing. Kim attended the launch of the sub, named Hero Kim Kun-ok after a North Korean naval officer who fought in the Korean War, on Sept. 6, according to the official [North] Korean Central News Agency.

Images suggest it is a modified version of the 1,800-ton Romeo-class sub with a displacement of 3,000 tons. A total of 10 missile launch tubes were seen on its topside deck.

But South Korean experts say the design is peculiar and the 10 missile launch tubes are incongruous with its relatively small size. They suggested the North was exaggerating its naval capabilities ahead of its 75th anniversary last Saturday.

Further doubts on the prowess of the sub from Tom Sharpe, a former Royal Navy officer who used to command an anti-submarine frigate, in the Telegraph:

The news that North Korea has modified an ageing Russian diesel submarine to fire nuclear weapons has been met with some mirth amongst the underwater community. The boat’s hull form now resembles a child’s drawing of a submarine, and it “will handle like a pig, dived or surfaced” according to my submariner friends.

So is this just a PR stunt by the North Korean regime or a viable platform for carrying nuclear weapons?

Let’s start with the Romeo class diesel-electric submarine on which it’s based. Romeos were built in the Soviet Union between 1957 and 1961 and in China between 1962 and 1984. Even back then, the Romeos were considered ‘noisy’ – relatively easy to detect and track. The whole point of a submarine is that its enemies don’t know where it is, so this is not a desirable characteristic.

North Korea imported seven Chinese-built Romeos between 1973 and 1975 and built a further 13 domestically. There isn’t any firm information on their operational state but ‘not very’ seems to be the consensus.

‘Diesel-electric’ is a commonly used power train in submarines, much the same as you would find in U-boats or Allied subs of the World Wars. You get batteries and electric motors for running when fully submerged, and diesel engines which can drive the sub faster and recharge the batteries. Diesel-electric remains the most common propulsion type in the world due to its relative simplicity and low cost.

Diesel-electric submarines have an Achilles heel, and it’s huge; more like an Achilles leg. Batteries cannot hold very much energy, so when fully submerged the submarine cannot move at all fast (except perhaps for a brief battery-draining sprint) and it has limited range.

To recharge its batteries or travel at speed the boat has to start up its diesel engines. Not only does this make a racket in its own right, but because diesels require air to work, the sub has to either surface or come to periscope depth and put a dustbin-sized snort mast above the surface that can be detected by radar or even seen. So for the entire period of the recharge, often many hours, the submarine’s acoustic, visual and radar signatures are all increased. This vulnerability is what drove the world’s better-funded navies to develop and build nuclear submarines, which can go fast and far while fully submerged, staying down for months on end if need be.

It is, in other words, effectively uselsss. All for show.

The newly-modified North Korean boat will be easy to track by any serious anti-submarine operator in the region. South Korean 214 submarines will have no difficulty at all tracking and destroying it if needed. Likewise the Japanese Soryu class are excellent and their lithium-ion batteries give them much better dived endurance than most diesel-electrics. A US Navy Virginia class boat would scarcely need to make an effort.

Submariners are a cautious bunch and generally shy away from saying that hunting other submarines is easy, but in this case, it really would be….

In the meantime, its ability to deliver Armageddon remains reassuringly remote. For now, the only risk this submarine poses is to the luckless sailors who have to go to sea aboard her.