AIP vs. nuclear submarines: No contest
Even as the world waits with great anticipation to see if the new diplomatic approach of the Obama administration lessens tensions throughout the world, many governments seek to gain advantages through arms purchases.
One of the key defense acquisitions of powers that are traditionally weaker than their adversaries is the submarine. Germany, it will be recalled, relied on the submarine as its primary offensive naval weapon in two world wars. Today, several countries, including those long considered U.S. allies, produce advanced diesel-electric and air-independent propulsion (AIP) subs for sale to other countries — including those long hostile to U.S. interests, or those which are sometimes tenuous allies.
Diesel-electric subs, or SS in naval jargon, are much more advanced today than those of World War II or even in the 1980s at the end of the Soviet empire. The Kilo class subs produced by the Russians today — and offered for sale to the likes of Iran, North Korea and China — are among the most modern when it comes to mating “old” power to advanced weaponry and detection systems.
But the problem with SS subs has been and always shall be limitations on endurance and the ability to remain submerged to extended periods. The Germans experimented with advanced systems at the end of World War II that led to the Guppy submarines that dominated U.S. and Soviet navies until the advent of the nuclear submarine in large quantities, beginning in the 1960s.
Most nations can’t afford nuclear submarines (SSNs), and the need to have better endurance led to the development of the AIP sub, or SSP in the Navy’s designation. The SSPs can stay submerged for up to two or three weeks before snorkeling or surfacing to recharge batteries.
France, Germany, Russia, Japan and Sweden are among those building AIPs, plus France and Spain, and Italy and Germany jointly build additional AIP types. Overall, there about a dozen nations producing submarines and offering them for export sale.
In naval exercises, there have been instances where SSP or advanced SS subs got the drop on U.S. SSNs or U.S. surface ships, leading some observers to conclude that these submarines are quieter than our SSNs. Combined with the smaller size and better ability to maneuver in shallow waters, these observers believe that our naval forces face a grave threat in a hostile environment. This leads a few observers to suggest that the Navy should resurrect the diesel-electric submarine as a less-expensive alternative to the SSN, trading quantity of SSPs for nuclear power.
Proponents of SSPs argue that with a price of as little as $250 million, compared with $2 billion for the new Virginia-class SSN, the Navy could get eight AIPs for the price of one SSN. The math may be undeniable and the advantages in some circumstances debatable, but for the Navy and its unique operating requirements, the case for a U.S.-flagged advanced SS or AIP sub is thin indeed.
Although the SSP is a major advance over standard SS submarines, the performance characteristics still pale compared with the SSN. The SSN easily outclasses the SSP in speed, endurance, weaponry and systems. For those suggesting the U.S. ought to build and acquire its own fleet of SSPs, a simple map exercise dispels this argument.
The U.S. mainland is bracketed by thousands of miles of ocean, and even our bases in Hawaii and Guam are vast distances from global hotspots. SSNs have the unlimited legs to surge anywhere in the world and the speed to do so quickly.
Guam, the SSN’s forward Pacific submarine base, is 3,500 miles west of Hawaii and 1,300 miles southeast of Japan. At flank speed in excess of 30 knots, an SSN can go from Pearl Harbor to Guam in about 4½ days. An SSP has a top speed of about 20 knots, but this is during a short-lived sprint. Long-distance cruise, using diesel power, is about 10 knots, according to technical specifications. The vaunted two-week endurance of an SSP is at slow speed of 5 knots or less.
An SSN can go from Guam to Japan in a little more than a day and a half; an SSP would require considerably more time at economical slow battery speed. These could be critical times in a crisis. A Guam-based SSN can surge to the Middle East, for example, quickly and without fueling. An Atlantic SSN, with a forward base in Diego Garcia, can surge to the Pacific. An SSP would take far longer to surge and be faced with refueling requirements at some point.
Furthermore, because the SSP has to snorkel to recharge, an adversary has the potential to spot the SSP.
Stealth is critical to submarines.
During the Falklands War in 1982, Britain said it had nuclear submarines in the South Atlantic deployed against the Argentine Navy, and one sank the cruiser Belgrano during the conflict. This prompted the Argentine Navy to return to port for fear that there were several speedy, stealthy British nukes in the area. This fear factor would have been greatly diminished had the British possessed and deployed only SSPs.
The SSN’s superior capabilities become obvious and the SSP’s deficiencies in comparison are clear.
Still, advanced SS and SSPs have their place. Early in his administration, President George W. Bush agreed to supply modern diesel submarines to Taiwan in an arms package. It wasn’t clear whether these would be advanced SS or SSP subs, and the transaction never took place because of objections from China. But the underlying rationale was that the diesels were required for Taiwan’s defense. And defensive operations are where advanced SS and SSPs are best suited, according to some experts.
According to these experts, the smaller subs are better for shallow waters close to home, where AIPs can lie in wait for a superior naval force and in which the defenders have limited or no air force or surface navy with which to defend home waters. The straits of Taiwan, Hormuz and Malacca are constrained, shallow and important oil and trade routes that can be shut down quickly by SSPs.
The South China Sea and Yellow Sea are two more strategically important bodies of water, the former with several disputed territories.
However, it must be noted that with some AIPs having a range of 12,000 nautical miles, this gives them very long legs — longer than the U.S. fleet boats of World War II. During the Falklands War, an Argentine Type 209 German-built diesel sub launched two separate if unsuccessful torpedo attacks on British warships. The sub got away undetected after a month evading anti-surface warfare vessels.
Supporters of the AIP argue that the SSP’s smaller size gives it an advantage in shallow water. This may be true in the context of deploying Special Forces from sub to shore, but even this is debatable when the Navy’s Advanced SEAL Delivery Vehicle (ASDV) and Swimmer Delivery Vehicle (SDV) submersibles, which are carried by SSNs, are used. The ASDV has a range of 100 miles, allowing the SSN to stand off shore considerable distance. Unlike World War II operations in which SEAL teams had to swim from a submarine to shore, the ASDV and SDV submersibles give them considerably more distance options with the important benefit that much more equipment may be deployed as well.
The long-range capabilities of today’s torpedoes, not to mention missiles, negate the requirement that submarines operate in shallow waters like the World War II SS boats did.
China is a perfect example of mixing advanced SS and SSPs with SSNs. The country has purchased a dozen Kilos from Russia and is building advanced diesels for use in its shallow homeland waters and those short distances in the seas off its east and southern coasts. But its blue-water submarines are SSNs and SSBNs.
None of this suggests minimizing the threat of the advanced SS or SSPs to the Navy’s surface fleet. On the contrary, the threat is real and growing as the number of advanced submarines grows in the hands of our current and potential adversaries. AFJ
Scott Hamilton is an analyst with the Leeham Co. (www.leeham.net).