The navies of the South China Sea have few good options to deter China from its aggressive territorial claims. And they will have even fewer options if competition ever turns to open conflict.
Vietnam’s six 4,000-ton (submerged) Project 636 Kilo-class submarines stand little chance of competing with China’s much larger submarine force, except perhaps in covert operations. But this would require piggybacking an all-electric commando carrier, which would seriously limit operating depth.
The deployment of midget submarines, on the other hand, could provide Vietnam an asymmetric advantage by employing lessons drawn from the past, revitalized by innovative new designs. “Midget submarine” does not describe just any small submarine; it identifies a specific type of boat designed to operate in coastal shallows, follow the contours of the seabed, and slip into harbors covertly to deliver weapons or combat swimmers. The Vietnamese Navy has a large and highly skilled force of combat frogmen who are well trained for such operations.
A South China Sea Dispute
The Paracel Archipelago in the South China Sea comprises more than 1,000 coral islands and reefs spread across 5,000 square nautical miles (nm) with a land area of less than 3 square nm total. It is about 200 nm southeast of China’s Yulin naval base on Hainan Island and about 240 nm east of Da Nang, Vietnam.
The archipelago is claimed by both countries, but in 1974, China established control of the Paracels through force of arms and the colonization of several islets (Woody Island being one of several examples), after which it claimed the entirety of the South China Sea. It has since been building additional military bases to reinforce this claim.
The Yulin base—less than 150 nm from Vietnam—can host submarines in difficult-to-attack underground shelters (a Type 093 submarine was spotted entering a tunnel in August 2020). Four 950-meter-long jetties fitted out to support multiple aircraft carrier strike groups have now been completed. In the event of fighting, the present Vietnamese military would have little ability to defend itself from Chinese naval forces there.
What Midget Subs Can Do
The sea around the Paracel Archipelago is 1,000 meters deep, enough for safe operation of nuclear-powered and diesel-electric submarines, which cruise well above the seabed. There is also a window to be exploited by the new generation of midget submarines rated for operation at such depths.
Taiwan and Vietnam both challenge the People’s Republic of China’s territorial claims, but neither can hope to compete directly with China’s naval power. Midget submarines could change that, however. World War II Japanese Kō-hyōteki midget submarines, including the famous 86-foot Type A, transited both the Pacific and the Indian Oceans riding piggyback on mother submarines to strike Pearl Harbor, Sydney, and Madagascar, the latter during the monsoon season. Also in World War II, British X-Craft minisubs were towed to northern Norway in 1943 to strike German surface ships after a voyage of 1,500 nm; and after Italian minisubs seriously damaged two Royal Navy battleships in the Raid on Alexandria in December 1941, the Italians made plans to piggyback midget submarines across the Atlantic to strike New York.
Unfortunately, that history has been forgotten today, and the potential of midget submarines has been mostly ignored until recently.
A new generation of midgets might carry eight combat swimmers, tubes for three 21-inch wire-guided torpedoes or submarine-launched SM39 Exocet missiles, four reloadable short-range 5-inch torpedoes with seekers that home on a target’s propeller, and ISR sensors. But, above all, such submarines would possess the capability to lay minefields in shallow water.
Vietnam’s small number of Kilo-class submarines cannot compete with China’s more numerous submarine fleet in most operations. The Kilos would have some use in covert operations, although these would require piggybacking an all-electric combat swimmer carrier that would seriously limit their operating depth.
U.S. Special Operations Command is developing the Dry Combat Submersible S351 Nemesis. These submersibles are nearing initial operational capability, but, unlike other swimmer delivery vehicles, they will be launched from surface ships, not by submarines, and will not have the capability to travel long distances by themselves.
The proposed midget subs instead would have diesel-electric propulsion, standard displacement of around 120 tons, the lead-acid batteries found on German Type 212 submarines, and an operating depth of 1,000 meters. For one design under consideration, experiments and calculations suggest a maximum underwater range of some 500 nm at 4 knots, 120 nm at 12 knots, and a snorkeling maximum of about 4,000 nm at 8 knots. Its most important capability would be to operate in shallow water and intrude into harbors, exploiting wrecks and obstructions to conceal themselves instead of avoiding them.
This would be guerrilla warfare at sea, which will require new doctrine and training of a sort different from the existing approach. The Vietnamese have already demonstrated mastery of such arts, and seeding even a few mines into the seabed would be enough to incapacitate a port during lengthy clearing operations. Leaving Da Nang to surface near Woody Island for a sniff, cruising on the surface for an hour, then disappearing before showing the flag off Hong Kong, steering on the surface for a few hours to dive again, skirting the edge of the continental shelf and nosing around next to Kee-Hung before heading home could be an important signal to China during competition below armed conflict.
If competition heats up, each midget could carry 12 bottom-influence mines, a handful of which could shut down Yulin Naval Base for months without the midgets ever surfacing to snorkel. Even the Port of Shanghai (1,300 nm from Da Nang) would be within reach.
Of course, it is for others to consider the political implications of such activities; the aim of this commentary is simply to consider the state of the art, explain what could be done today by an innovative navy, and suggest ways to exploit the opportunities offered by safe sailing over such a wide range of depths. The focus has been on Vietnam’s claim to the Paracels, but there are implications for the navies of many countries.