The realities of the challenging operational environment meant that early SSBNs required higher speeds and deeper diving depths to avoid detection and thwart attacks by torpedoes and depth charges. The ability to dive deep can provide significant tactical advantages. It can allow a submarine to get below the acoustic “layer” and minimize the chance of detection. Going deep to evade torpedoes and also can improve the probability of outrunning a torpedo with thermal propulsion. Although SSBNs normally operate at slow speeds to minimize their acoustic signature and avoid detection, periods of high speeds can be extremely useful for breaking contact from an enemy submarine and can obviously be helpful when trying to outrun a torpedo.
Early SSBNs also required the means to defend themselves against SSNs (as submariners are fond of saying, the best evasion device is a well-aimed Mk 48 torpedo). During the Cold War it was quite conceivable that a Lafayette -class SSBN might find itself slugging it out with a Soviet Victor -class SSN in the North Atlantic as part of a war that might be leading to an exchange of strategic nuclear weapons.
America’s first SSBNs were actually built by modifying Skipjack -class submarines to accept a new section of missile tubes. The first two submarines of what would become the George Washington -class actually had to be cut in two before mating a 141-foot section that housed the missile tubes. 3
Future of Strategic ASW
Two developments in the last two decades of the 20th century significantly decreased the ASW threat against U.S. missile subs. The advent of the Trident C4 in 1979 and D5 in 1989 (with a range of at least 4,000 miles) allowed our SSBNs to operate in patrol areas measured in tens of millions of square miles and at distances well beyond the range of Soviet ASW aircraft, and even outside the “effective” operational range of most Soviet surface and submerged ASW forces. Second, the fielding of ultra-quiet Ohio -class submarines with very capable sonar systems made it extremely difficult for a Soviet attack submarine to get close enough to detect a Trident on patrol. The Ohio class used a variety of quieting technologies (i.e., natural-circulation reactor plant, advanced sound-dampening equipment mounts, and an array of installed noise-monitoring devices) to dramatically decrease its acoustic signature compared with previous SSBNs.
The range of Trident missiles and the extremely low acoustic signatures of the Ohio class reduced the threat of “strategic ASW” to essentially nil. Strategic ASW is a conscious effort to find and destroy SSBNs during the conventional phase of a war between nuclear-armed powers. 4 The concept of strategic ASW was debated during the Cold War regarding both its desirability and feasibility. As the haze shrouding the Cold War lifted, little evidence emerged that the Soviet Union, with one of the largest and most capable navies in history, ever seriously planned to mount a strategic ASW campaign. 5 Instead, the Soviets decided to employ their limited ASW capabilities to create bastions to protect their own SSBNs against America’s deadly Sturgeon - and Los Angeles -class hunter-killer submarines. 6
Looking ahead to the operational lifetimes of the Ohio -class replacements (roughly 2030 to 2080), the probability that Russia or China would develop the capability and will to mount a strategic ASW campaign seems low. From a capabilities perspective, their navies will remain junior partners to their land forces and are unlikely to be given the significant resources required to field the sensors, basing infrastructure, and the number of long-range ASW-capable ships, submarines, and maritime patrol aircraft needed to hunt U.S. ballistic-missile subs. 7 In May 2011, the House Armed Services Committee published the following assessment, which is likely shared by both Russian and Chinese naval leaders: “Ballistic missile submarines are the most survivable asset in the arsenal of the United States . . . these submarines are virtually undetectable to any adversary and therefore invulnerable to attack [emphasis added].” 8
Regarding will, Russia and China will likely conclude that strategic ASW operations would have an unpredictable or escalating effect on hostilities with the United States and therefore would be undesirable. More than likely, both of these U.S. peer competitors will, like the Soviet Union, make a decision to employ their limited ASW forces to protect their SSBNs and homelands from attack by an armada of extremely capable U.S. and allied naval forces.
Thrifty Design Options
America probably cannot afford to build another generation of multimission-capable SSBNs. Significant savings potentially can be achieved by designing a new SSBN for a single-mission and -operating environment, and nothing more. Three areas ripe for reconsideration are requirements for speed, depth, and defensive weapon systems.
One of the most significant submarine cost drivers is its propulsion plant. The capacity and cost of the propulsion system is intimately related to maximum design speeds, since power must be increased as a cubed function of speed. (Doubling maximum speed would increase required power by approximately a factor of eight.) For example, decreasing maximum design speed by 25 percent (for example, from 20 knots to 15 knots) would reduce the required propulsion power approximately by half. With essentially no strategic ASW threat, the SSBN(X) should be able to forgo higher speeds that would provide only marginal increase in survivability when evading torpedoes or trying to break sonar contact from an enemy submarine.
The cost of building a submarine also is closely tied to how deeply it must dive. As stated previously, the ability to operate at great depths can help a submarine avoid acoustic detection and evade torpedo attack. Thermal propulsion torpedoes, as opposed to electric torpedoes, must exhaust their combustion gases against the ocean’s pressure. As the torpedo operates deeper, the backpressure increases, and the torpedo engine’s efficiency, and therefore its range, are decreased. However, the significantly reduced risk of strategic ASW may allow for building a submarine that cannot dive as deeply as previous SSBNs. In any case, because of their need to receive orders from the National Command Authority, especially during periods of heightened tensions, SSBNs are forced to operate at relatively shallow depth despite being equipped with tethered communication buoys and floating wire antennas to receive very-low frequency communications.
The required operating depth is also determined by the submarine’s maximum speed. Operating depth must be deep enough for the submarine to pull out of a jam-dive casualty before breaching her watertight integrity. A jam-dive occurs when a submarine’s diving control surfaces fail in a “dive” orientation and cause her to nose-down in an uncontrolled fashion. The faster the submarine is traveling at the beginning of the casualty, the deeper she will dive before the descent is arrested using astern propulsion or an emergency blow (rapid dewatering) of ballast tanks. Reducing the SSBN(X)’s maximum speed, as suggested here, would facilitate decreasing her required design depth and thereby help reduce material and fabrication costs. 9
Although tantamount to heresy, the cost of equipping America’s next SSBN with torpedoes may not be a sound investment. The boat’s stealth is its first and best line of defense. If she does end up in a dogfight with an attack submarine, her ability to perform her strategic mission is seriously compromised. Plus, as stated earlier, there is a low probability that future adversaries would have the means and will to hunt for quiet U.S. SSBNs in their far-flung operating areas. (It is interesting to note that neither B-2 nor B-52 strategic bombers are equipped with defensive missiles, guns, or cannon.)
Removing the requirement to equip SSBN(X) with tactical weapons could save a variety of costs. It would avoid the design, construction, and maintenance of the torpedo room, torpedo-handling equipment, torpedo-launch systems, and fire-control systems. Additionally, the design change would eliminate the time-consuming and repair-limiting evolutions of loading and unloading war-reserve and exercise torpedoes. Torpedo-handling evolutions can involve up to a dozen members of the ship’s force as well as sailors supporting the operation on the pier. Handling weapons on an