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Total Ship Survivability and Surface Stealth

Wavelengths: An Employee's Digest of Events and Issues (NAVSEA Carderock)

October/November 2002

By Jim King; synopsized by William Palmer

WEST BETHESDA-Survivability is one of the most important attributes of surface ships. It is especially critical in these days, as the public becomes ever more sensitive to the deaths and injury of our Sailors, while our ships become more expensive. Total ship survivability (TSS), a systems-engineering approach to survivability, ensures a more efficient incorporation of survivability into new ship designs and acquisitions. Stealth is a major element of survivability because it helps to prevent damage and reduces demands on defensive systems.

A ship can survive combat either by avoiding damage or by continuing to function after damage. Damage can be avoided by preventing attack, by a "softkill" employing electronic warfare or jamming of an attacking weapon, or by destroying the attacker. If damaged by attack, the ship continues to function by minimizing vulnerability and providing safe, efficient, and rapid recoverability of both the ship and its functions. If all else fails, the ship must provide safe abandonment by the crew.

Ship Survivability Timeline

The ship survivability timeline is commonly divided into two phases. The first phase is the Kill Chain, which emphasizes hit avoidance. The second phase is Damage Tolerance, which limits damage from a successful attack and recovers from it. First, an enemy must detect our ship, and then he must identify it as a target worth an attack. This may be done, for example, by a land-based surveillance station, or a maritime patrol aircraft. Second, he has to track our ship accurately and precisely enough to launch an attack because the attack platform has limited range and time. Third, the attacker must be able to engage us with its own sensors, which requires detection, identification, and tracking. Fourth, the weapon must engage the target through impact. It also has to detect, identify, and track us throughout its attack.

Obviously, it is best to break the survivability timeline as early in the process as possible. If an attack is successful, we can try to limit the extent and severity of damage. The provisions for limiting damage are a function of the ship's design. Compartmentation, redundancy, distribution of systems, selection of materials, and armor contribute to this. Then, the crew prevents further damage, such as from fire and flooding, to save the ship, and recovers functions, including maneuverability, crew support, and even combat capability. As crew sizes diminish, the ship must be more self-contained in damage prevention and function recovery because human-intensive methods will not be possible.

The various means to prevent or survive an attack can complement each other. For example, if an enemy platform can attack our ship at a reduced range, or if it takes longer to identify us, our ship's weapons may make a successful attack on that platform. Inaccuracies imposed on an attacking weapon may limit damage. And, inherent ship design factors may make recovery less stressing and faster.

It is important to recognize that not all attacks are made by launching a weapon from a platform. Some small boat or terrorist attacks, for example, are quite different because the timeline may be compressed, and the ranges quite close. Mines present a special case, lying in wait for an unsuspecting ship and following an abbreviated Kill Chain. Influence mines, in particular, detect and activate, may identify, and engage a ship in a short period of time. Contact mines do not follow a Kill Chain. Submarines, on the other hand, may be directed from another source, and so may follow the pattern described, but may also perform the entire Kill Chain independently.

Some of the tools promoting improved survivability are material, tactics, and training. The crew must be trained to take greatest advantage of features provided for recoverability. Three elements enhancing recoverability are a well-designed and constructed ship, a captain who trains and leads his crew after damage, and a well-trained, courageous crew who fights to save their ship and shipmates.

Stealth and the Ship Survivability Timeline

Although we attempt to measure signatures in absolute quantities, no target is physically seen this way. It is always seen as a contrast against a background, which may be natural, as in sea clutter or the infrared background scene, or synthetic, as in an electronic jamming signal.

As discussed earlier, it is best to break the Kill Chain as early as possible. Consider how each link of the chain can be broken and how stealth can contribute to breaking the chain:

  • Detection: The observer makes a detection when the signal from the target is sufficiently greater than the clutter to allow the observer to confidently declare a detection. So, in order to avoid detection, the target does not have to be invisible, but merely have signatures small enough to hide in the background. Historically, this was done by hiding in fog, beyond the horizon, or behind topographic features.
  • Identification: The observer now must determine that the target is a ship that he wants to attack. He should be certain that it is not a neutral or friendly ship, a decoy, a commercial or fishing vessel, or an unimportant naval ship. We can delay or foil identification by modifying our signature to appear to be a much smaller or less threatening ship. Again, historically, ships would use paint schemes, false structures, or false flags to conceal identity.
  • Localization: Controlled signatures, combined with the ship's mobility, make localization difficult. The data passed to the attacking platform are inaccurate, requiring additional search time. In addition, ships with low signatures may appear only intermittently, increasing inaccuracies.
  • Targeting: The attacking platform has to detect, identify, and localize the ship, usually with a less capable system than used in detection, although at shorter range. The attacker can be confused or distracted away from a ship using decoys or various electronic warfare tools. Lower signatures force an enemy to use smaller targeting ranges, exposing the attacker to the ship's defensive weapons.
  • Engagement: Against a low signature ship, the weapon is far less likely to acquire and track the ship. Countermeasures can be used much more effectively to seduce a weapon away from the ship once it has begun to track.

Just as resource limitations require tradeoffs among the components that contribute to survivability, a balance among signatures is required. Essentially, all signatures should be reduced to levels where they are equally useful (or useless) to the attacker and act as a force multiplier for the ship's combat systems. It is not necessary that the exploitation ranges for all signatures be reduced to the same value, but to ranges that make their operational use by an enemy impractical or risky.

Signature control also reduces demands on defensive systems. Repeated studies have shown, for example, that ships with lower signatures require fewer self-defense ammunition rounds. Ships with reduced signatures also enable the use of less costly countermeasures, and effectively enhance those countermeasures' performance.

Implications on Ship Requirements

As requirements are developed, we must consider what we hope to accomplish with either sturdiness or stealth on a particular ship design before specifying levels of performance. Some examples for stealth application are given below:

  • Special Warfare Craft: This craft needs to avoid detection. It would be designed for low detectability across the spectrum. Primary emphasis would be on nighttime operations.
  • Submarine: Periscopes and masts are extended in many conditions. Thus, the submarine needs to avoid detection by emphasizing low radar cross-sections (RCSs) and visual detection night and day. The submarine may also need to surface, in which case signature requirements would emphasize night operations for the exposed sail in visual and infrared spectra and low RCS.
  • Corvette: This ship might want to emphasize difficult identification and take advantage of mobility together with signatures to make localization difficult and improve countermeasures effectiveness. For some missions, under limited environmental conditions, such as at night, it may want to avoid detection across the spectrum.
  • Cruiser/Destroyer: These ships may take advantage of signatures to complicate identification and achieve some advantage in localization under many conditions. They emphasize the targeting phase because of the opportunity to destroy an attacker by drawing it in. Countermeasure effectiveness is also improved.
  • Carrier: The carrier would emphasize countermeasure effectiveness because of its size and operational mode. It might also be able to avoid detection or identification under very limited environmental and operating conditions.

Managing Ship Design to Achieve Survivability

The submarine community has developed a disciplined, comprehensive organizational approach to stealth that has enabled our Submarine Fleet to stay ahead of evolving threats. A similar approach in the surface community would yield a similar advantage.

Sturdiness and stealth should be considered as complementary, not competitive, attributes. They should be designed into a ship in such a way that each takes the greatest advantage of the other. Neither sturdiness nor stealth should be considered a characteristic to be traded off or worked into the design. Because they are integrating functions, they need to be fundamental attributes of the ship.

Stealth and sturdiness should also not be considered only at the ship level. The ships in a battle group, even in the Fleet as a whole, depend on the survivability of the other ships. This implies a greater-than-normal level of interoperability, that requirement decisions be made Fleet-wide, and how shipboard sturdiness and stealth characteristics will be utilized.

We must continually strive for better survivability at lower cost. This will require considerable investment in the technology. The Department of Defense Appropriations Committee recognized the need for investment in survivability technology when it wrote, ".The Committee is especially concerned about technologies which need to be supported over the long-term because they (1) are essential national naval responsibilities, (2) have the potential to have a major impact on the Navy After Next, and (3) are not likely to be supported by the private sector. An important set of technologies which falls into this category is naval ship technologies, which includes hydrodynamics, machinery, electrical and propulsion systems, stealth, ship protection and structures, and advanced seaborne materials. To maintain U.S. technological superiority in these areas, the Committee recommends that the Administration give serious consideration to the relationship between increased and consistent funding in science and technology and the maintenance of U.S. technology superiority, and reflects these considerations in future budget submissions ... "

These above-mentioned considerations must be carried forward into operation. They each require training. Sturdiness emphasizes damage control and recoverability training, while stealth emphasizes configuration management and tactics training. Systems must also be maintained, acknowledging that minimizing maintenance requirements is one of the major goals of the technology. Independent survivability authorities are necessary at the requirement, technology, and ship design levels to advocate and direct the advancement of these important Total Ship Survivability capabilities of our ships and Fleet.

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