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China-Taiwan: Beijing's new attack submarine could change the game

Stealthy sail shape as seen on China's new attack submarine. It could offer an advantage against the US Navy in the coming struggle for Taiwan
Stealthy sail shape as seen on China's new attack submarine. It could offer an advantage against the US Navy in the coming struggle for Taiwan

A new Chinese attack submarine is the first submarine in the world to feature an important enhancement to its stealth qualities: an oddly-shaped sail, or conning tower.

The upgrade isn’t just a boon to the 60-person crew of that one (so far) Type 039 sub. It might also signal a new standard feature on future Chinese submarines – one that could help them avoid detection by the US and allied fleets.

That, in turn, could give the People’s Liberation Army Navy a better chance of staving off American and allied intervention in the event that Beijing makes good on decades of threats and launches an invasion of Taiwan.

The basic Type 039 submarine is unusual only for being the first diesel-electric sub to be fully developed in China rather than based on a design from aboard. It uses a modern teardrop-shaped hull for better underwater performance, but otherwise it’s a largely standard diesel boat, badly limited by the fact that it has to run on batteries whenever it’s fully submerged and thus lacks speed and range. Subs like this have to spend prolonged periods “snorting” at periscope depth with an air-intake mast raised in order to recharge batteries.

US Los Angeles class submarine with conventional, vertical sail or conning tower. China's new stealthy version could offer an advantage in a future battle for Taiwan
US Los Angeles class submarine with conventional, vertical sail or conning tower. China's new stealthy version could offer an advantage in a future battle for Taiwan - MC3 Naomi Johnson/US Navy

As new Type 039s have been built, improvements have been made. Western analysts classify the newest boat as Type 039C or D, and it’s thought that this is much quieter and stealthier underwater than the first of the class. It’s also believed that the latest 039s have so-called “air independent propulsion”. This is one kind or another of conventional engine or motor which can run even with the sub fully under: typically this is done by carrying supplies of oxidiser or oxygen so that no air intake above the surface is needed. Such AIP systems aren’t as good as nuclear propulsion, which allows a submarine to stay down for months going at full speed the whole time if need be, but they are much better than batteries. But AIP is quite common in non-nuclear subs nowadays.

What the latest 039 has that no other sub in the world does is this new sail shape. H.I. Sutton, a reporter specializing in naval subjects, was among the first to report on the vessel. Sutton was also one of the first foreign observers to confirm the new sail’s purpose.

Where most submarines have straight sails, which contain the vessels’ periscopes and radar masts, provide a way in and out of the subs and also help stabilize them while submerged, the new Chinese sub has a sail with distinctive angular kinks in it.

Sutton found references to the modified sub in an article by Chinese academics that appeared in a recent Polish academic journal. According to Sutton, the article confirms that the angles reduce the sub’s signature on active sonar, thus making it harder for enemy subs, surface ships, patrol planes, helicopters and seafloor sensors to detect and identify the Chinese vessel.

Greater stealth is a main objective of Chinese submarine-designers. And for good reason. As recently as 2015, the US Office of Naval Intelligence assessed the 61-strong PLAN attack sub force as having a “limited mission set.”

Where the US Navy’s own 50-plus large nuclear-powered attack submarines can strike targets below or on the surface of the sea or on land, anywhere in the world, the PLAN’s smaller submarines – all but a few of them non-nuclear – used to be mostly for coastal defense. They couldn’t safely sail into deep water to engage enemy fleets on their watery turf.

That’s changing – and stealthier subs are one reason why. When the US Defense Department released its annual report on the Chinese military earlier this year, it warned that the PLAN “has placed a high priority on modernizing its submarine force.”

With their combination of stealth and firepower, submarines are uniquely powerful. When the Center for Strategic and International Studies in Washington, DC war-gamed a Chinese invasion of Taiwan early this year, it found that the US Navy’s submarines, working in conjunction with US Air Force bombers, stood a good chance of sinking the Chinese invasion fleet and saving Taiwan from authoritarian takeover.

“Submarines were able to enter the Chinese defensive zone and wreak havoc,” CSIS noted.

China’s own submarines performed two main roles in CSIS’s conception of a war over Taiwan. They tried to intercept American and Japanese subs from entering the Taiwan Strait in order to attack the Chinese invasion fleet. At the same time, the Chinese subs attempted to sink US and allied surface ships steaming toward Taiwan.

Neither effort succeeded – not in the 2026 timeframe that CSIS set its war game in. American and allied forces are adept at finding and sinking enemy submarines. That anti-submarine prowess is a hedge against a growing Chinese sub fleet. One that won’t disappear overnight.

Even with the recent alterations to that one Type 039, the PLAN’s “submarine quieting technology remains immature.” But it’s improving fast, and in ways that so far are unique to the Chinese fleet. No other country has completed a sub with the same stealthy sail as found on that Type 039, although Germany and Sweden each are working on it, too.

Equally ominously, the PLAN is setting up extensive infrastructure for building and maintaining submarines. Its attack sub fleet is already the biggest in the world by a small margin, if you count non-nuclear boats – and that margin could change fast, with little warning.

Right now, the Chinese submarine force “continues to grow modestly as it works to mature its force, integrate new technologies and expand its shipyards,” the Pentagon reported. In the last two years, the PLAN has greatly expanded the Huludao shipyard on the Bohai Sea in northern China. It’s there the Chinese fleet builds its best nuclear-powered subs.

The construction of new subs could ramp up soon. By 2035, the PLAN could have 74 attack submarines while the US Navy still has just 50. More than a few of the Chinese vessels might have the added stealth features, and a greater proportion of them would be nuclear powered.

The US and its allies are working to build their own naval power to counteract that of China. The Aukus pact will see at first US-built nuclear powered submarines operated by Australia, then joint US-Australian nuke boats. Meanwhile the Royal Navy will soon base a nuclear powered attack sub in the Far East, and Taiwan itself has just built a new AIP boat of its own, with help from various Western nations.

The question is – will the US and allied efforts be enough?

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