North Korea has a fairly large submarine fleet, as many as 70 antiquated diesel-electrics. In stealth or submerged range, none of them compare to Germany’s modern reinvention of the non-nuclear submarine, the Type-212, and Sweden’s Gotland class. These submarines use AIP, air-independent propulsion. Relieved of the necessity to recharge motive batteries by surfacing or snorkel, they have submerged mobility similar in character to nuclear submarines.
Various reports suggest that members of the above classes sank three U.S. aircraft carriers in mock exercises. None of the reports have been substantiated by the U.S. military. If the reports are approximately true, they are exceptions to the remarkable transparency of U.S. military self criticism. While official substantiation of these incidents would not endanger lives, it would endanger the congressional budgetary process that maintains the surface fleet.
All militaries, the U.S. included, have been subject to shock of new vulnerability similar to the above. The 1982 Falkland War sinking of the British destroyer H.M.S. Sheffield, by a French Exocet missile, is a case in point. Even though the precise characteristics of the French missile were known, and available for simulation, serious consideration by Western navies required a catastrophe. Curiously, the earlier sinking of Israel’s Eilat by a Russian Styx missile was not enough to trigger this.
To the credit of the U.S. Navy, the apprehension of inadequate torpedo defenses has not required a catastrophe. The mock sinkings were enough. A crash program, the Anti-Torpedo Defense System, is partly functional on five attack carriers. Carriers are distinguished as high value targets. But the distinction is obsolete. Today, all naval combat ships are high value. The days are long past when a destroyer could be manufactured in less than a year. The weapon systems contained by the hulls are too complex. Large hulls and superstructures are required to host these systems.
The general conclusions of the U.S. reviews were:
- Towed sonar arrays, the mainstay of detection, are not effective against AIP submarines.
- Nuclear attack submarines, with the ability to deploy and orient sensor arrays at varying depths, are more effective. Compared to noisy surface ships, the awareness of the attack submarine is enhanced by the quietness of the submarine itself. This facilitates patrol of a volume of water with reduced chance of detection by the opposing submarine.
- Passive defense, which includes screening of a high value ship by lower value ships, is ineffective. Part of this owes to the fact that an Arleigh Burke class destroyer is not a low value target.
- Active torpedo defense is a requirement.
But is the sophistication of an AIP submarine required to sink a ship? In 2010, a primitive North Korean midget submarine, with limited range and negligible endurance, sank the ROKS Cheonan. The location was less than 100 miles from an ongoing joint U.S.-South Korea antisubmarine exercise. Perhaps it is not coincidental that Kim Yong Chol, credited by some for the sinking, was (Reuters) on display at the Olympics closing ceremony.
In the case of hostility with unlimited rules of engagement, the strategy of the Allied navy would be to decimate the opposing submarine fleet faster than the “replacement rate”. This was the essence of the Battle of the Atlantic. The losses table is telling. Between 1939 and 1945, about 14.1 million tons of Allied shipping was lost to U-boats. Although massive technology deployments made successful U-boat attacks increasingly unlikely, Allied losses ceased only when the U-boat fleet had been effectively eradicated. This would be more clear in the historical record if the sunk ships had been of high value. But Liberty ships were built in less than a month.
Although the German U-boat, and the similar North Korean submarines, have limited mobility while submerged, they share in common the ability to lay in wait, with absolute silence, subject only to the limitations of battery charge and breathable atmosphere. In this state, the submarine is detectable only by active sonar in circumstances manipulated by chance. The water column itself protects a submarine from detection by reflecting, refracting and redirecting sound in ways difficult to unravel.
So a program of high-seas interdictions involves complex hazards analogous to those of recent and current limited wars. The Battle of the Atlantic was not limited war, but the deployable assets and goals of the interdiction program are just as asymmetric:
- The U.S. desires only to interdict North Korea shipping.
- North Korea wants to raise the cost of this to the unbearable level.
- Exposed U.S. naval targets are high value.
- Concealed North Korea naval targets (submarines) are low value.
- Destruction of North Korea naval targets is preferably avoided as an escalation.
- Destruction of U.S./Allied naval targets is a goal.
- In unrestricted conflict, U.S./Allied forces have overwhelming advantage.
- In conflict restricted to exclude proactive destruction of the North Korean submarines, North Korea may perceive an advantage.
- U.S. / Allied naval assets have high mobility.
- North Korea naval assets have limited mobility.
- Q-ships are a possibility.
The above admits the possibility of a shock of new vulnerability, particularly if operational planning is manipulated by diplomatic concerns.
In the Battle of the Atlantic, German U-boats, as a “wolf pack”, were pre-positioned so the target convoy would intersect the path of the U-boat. North Korean submarines are similar in capability, slow, noisy and detectable when they move rapidly, yet silent in wait. This inspires a reverse tactic for North Korea., with the Allied warship lured to the submarine. By coordinated action, a North Korean cargo ship acts as bait, sailing “suspiciously”, in a track intersecting a North Korean submarine, as many times as required to make the kill.
Quoting the Reuters article,
Some U.S. officials believe the risk could be minimized if Coast Guard cutters, which carry less firepower and technically engage in law-enforcement missions, are used in certain cases rather than warships.
Unless other assets are deployed in combination, this idea, prioritizing appearance over firepower, ignores what we have learned of North Korean psychology. Temperate rules of engagement are unsuited to this adversary. Perhaps those officials need a reminder. Perhaps they should take instruction from Hannibal Lecter’s artful escape.
Since the (Stars & Stripes) “can-do” culture of U.S. Navy is reluctant to decline a job, beware the shock of new vulnerability.