Sensor, electronics, and weapons technologies have improved dramatically since 1945, making warships deadlier than ever. At the same time, however, combatants have become more susceptible to dramatic damage if hit today than their World War II counterparts. The uncertainties of future warfare in the littorals, with the high risk of surprise attacks, dictate we build vessels that can take punishment—and keep on fighting.
Lately, the pages of Proceedings have been filled with calls for "rebalancing the fleet" to ensure access to and dominance of the littoral battle space.1 A fleet mix of "Economy A" and "Economy B" ships has been proposed to accomplish this. The Economy A ships are envisioned as economical power-projection ships, and the smaller Economy B ships are to provide risk-tolerant access to the littorals (i.e., the Streetfighter concept). A necessary characteristic of these ships is "sturdiness." The word sturdiness can be defined several ways, but here it refers to the capability of a ship to return fire after taking one or more missile hits.
Presence and operations in hostile littorals are indeed high-risk, and this—coupled with a political climate of low tolerance for casualties—points toward sturdy combatants when the fleet is rebalanced. Not generally known, however, is that sturdiness in combatants in the missile age can be attained only by radical changes in ship designs. It is true that sturdiness always has had a price, and the price would increase with the radical changes needed. But its value has risen significantly because of changing missions and rapidly developing weapons technology. In missile warfare, sturdiness is, in fact, a significant multiplier for the defense, and it should be considered along with all the other primary ship characteristics when new ship types are planned for the "fleet after next." The past approach to "sturdiness"—leaving it as an engineering problem that must be fit into a fixed-budget design—must be changed.
Why Sturdiness Is Needed Now
With the advent of missiles and high-tech electronics, combatant designs changed from being weight-critical to volume-critical. Much of the high-tech gear has been accommodated high in ships' superstructures, where heavy protection is not practical. Ships rely on active defense for protection. This status may have been acceptable in the days of the Cold War with its blue-water missions. When operating in the littorals, however, with clutter from land and commercial traffic, hidden enemies on sea and land, limited reaction time, problematic rules of engagement, and untried tactics, the old ways of doing things may not be acceptable. The risk of taking hits from surprise attacks is multiplied and even inferior opposing forces can cause serious setbacks in coastal areas. Unless we are prepared to accept losses or severe damage, combatants must be able to take hits.
Other forms of future surprises can emerge through technology. Even if our combatants were updated quickly, their effectiveness against an inadequately known opposition cannot be predicted—at least until the shooting starts. In addition, weapon and defense systems are becoming increasingly high-tech and computer-based, and complex systems often break down. Similarly, human operators also can fail, especially under the combined effects of limited realistic training and the strain of combat.
The vision of a perfect defense that can prevent all missile hits is not realistic. The results of hits can be severe. We need only recall what happened to the Israeli Eilat, the Pakistani Khaibar, the USS Worden (CG-18), HMS Sheffield, HMS Conveyor, the USS Stark (FFG-31), the Iranian Sahand, and the Turkish Mauvenet. These ships all were sunk or severely damaged. The hits on Sheffield and the Stark demonstrate clearly the danger of uncontrollable fires, which can be especially bad when induced by leftover propellant from missiles fired from short range. In fact, both of these ships were done in by fires—rather than by the damage from warhead explosions (some of the hits involved dud warheads that did not explode). None of the ships mentioned here had any special features to provide sturdiness against missile hits.
The Challenge of Sturdiness for Missile Combat
After Operation Crossroads in 1946 (the U.S. Navy's first nuclear tests against ships) it was generally believed that sturdiness against nuclear weapons was impossible to attain. Research in the 1950s and 1960s into weapons effects and damage potential showed otherwise, however. It actually was found that, with relatively minor effort, ships could be hardened to reduce damage ranges by about 75%. This had significant consequences for tactics that could be used for the nuclear war at sea contemplated at the time. Similarly, when the missile age evolved, it was widely perceived that sturdiness against antiship missiles was impossible given the accepted norms for combatant designs. But research has shown that improvements in sturdiness against missiles are possible as well. In question is how much better present combatants can be constructed, and how much change is needed against future missile threats to make a significant difference. This is not a simple matter—it requires "passive protection," and this is not a stock item that can be fit in readily, nor can proven designs be created out of thin air. Designs need to be developed to ensure protection against future threats.
To be effective, a passive-protection design must consider all current and future potential enemies' weapons' effects and their damage capabilities. These effects will vary with warhead size, its type and fuze, hit location, and with ship construction. A considerable variety of missile and warhead designs can be found in use, ranging from those designed to explode after penetrating the ship (semi-armor-piecing) to those designed to detonate outside (blast, fragmentation, and shaped charge). The latter may have proximity or contact fuzes, or both.
The sizes of current antiship missiles and their warheads vary considerably as well. In general, the smallest are antiair missiles used in a surface-to-surface mode, with warheads less than 100 pounds. The largest missiles may have warheads approaching a ton. The most common type probably is the semi-armor piercing, which, for its size, will cause the most structural damage because it is surrounded by the ship structure when it explodes. The Exocets used in the Falklands and Gulf wars were this type. Fragmentation warheads can do extensive damage to topside equipment and personnel when they explode over the ship. An example of this occurred on the Worden when a Shrike missile damaged her and put her out of action. Shaped-charge warheads can be particularly damaging. They are similar in function to antitank charges but several times bigger. They explode on first contact and cause damage by jet penetration and blast. They have a metal-lined cavity in the front of the warhead, which produces a hyper-velocity metal jet (Mach 20 to 30) capable of penetrating heavy armor or any other materials they encounter within the ship. Because of the great velocity of the penetrating jet they can ignite stowed on-board ammunition unless it is protected appropriately.
History is replete with incidences of exploding onboard ammunition that destroyed ships or exacerbated the damage caused by attacking weapons. A few of the better known cases are the USS Franklin (CV-13), Liscombe Bay (CVE-56), Shaw (DD-373), and Halligan (DD-584), and HMS Hood and Barham, all from World War II, when all the hits occurred in random locations. Today's stowed missiles are even more volatile than the ammunition of that war, and the weapons of the future could be precision-guided and aimed at specific shipboard locations. Except for this mechanism, missiles are far less efficient in sinking ships than torpedoes, because they hit above the waterline. In general, small ships are easier to sink than big ones.
Future warheads could employ explosives that enhance the desired damage more effectively, and they could employ more effective configurations. As long as they use explosives, however, they can be expected to cause damage in ways similar to those of current weapons. Future missiles could be different from today's; they can be expected to be stealthier, faster, and more precisely guided, all of which will tend to give them a higher hit probability. It is unlikely that future missiles would be made bigger to increase their damage capability, for greater size would be counterproductive to making them faster and stealthier.
The challenge of providing passive protection is to contain inevitable damage in a way that prevents impairment of ship functions. Two different approaches to incorporating effective passive protection can be followed. One is to adopt the "citadel" concept used in battleships, where all vital components were protected behind armor amidships (gun turrets outside the citadel also were heavily armored). Battleship-type armor would not work, but new versions of a protective system against missiles could be developed through research. It would require significant space, but without the weight of heavy armor—for that reason it will require a rather large ship. The concept has the advantages that personnel would be protected along with combat systems, the propulsion system, and ammunition, and the need for making individual systems survivable can be de-emphasized. In addition, the inevitable damage inflicted by hits could be kept near the exterior of the ship and fires could be prevented from spreading to the interior. Sensors outside the citadel would be redundant and reduced in number by using multifunction antennas.
The alternative approach is to allow a hit to do its damage in the interior and rely on complete redundancy of all vital systems with adequate separation of parallel branches to maintain functions. Personnel casualties would not be prevented. Like the citadel, this protection concept also would require a larger ship, in this case to accommodate the redundant branches and provide a structure large enough to absorb some damage without the ship breaking apart. The additional gear required for redundant systems would add to the cost. There is plenty of room here for development of new system architectures, perhaps miniaturized, that can withstand the violent disruption of branches without a failure of the total system. Application of this principle produces systems capable of reconfiguring themselves after parts are cut off. Like all other important systems, the topside sensors would be redundant. To preclude a profusion of vulnerable topside equipment, they would be reduced to the minimum possible by using multifunction antennas. The all-electric ship proposed for the Zumwalt (DD-21) class appears particularly well suited to support truly redundant systems. The redundant ship concept has two potentially vulnerable features. One is the magazines and other ammunition stowage. They cannot be protected through redundancy, but must have special protective systems. Similarly, the redundancy principle will not provide protection against fires. Fires started by the hits must be controllable, or the ship could be put out of action anyway, like the Stark and Sheffield. This requires fire-fighting systems that are effective against propellant fires in a damaged ship.
Even with the required research and development carried out successfully, it is doubtful that a combatant of the redundant-systems type can be made capable of taking much more than a few significant hits before she is put out of action. Of the two approaches to passive protection, the citadel type is probably the least known in terms of overall impact on ship design, but it also has greater promise and potential flexibility than the redundancy concept. The size of ship required to incorporate effective passive protection has not been determined, but a ship of more than 12,000 tons seems likely. The larger the ship, the smaller will be the percentage portion that is inevitably destroyed, and small ships cannot be protected effectively against all weapons.
Sturdiness Is a Multiplier for Defense Effectiveness
Predicting the future value of passive protection is impossible unless we can predict future engagements and all their details. We can, however, estimate the conditions under which passive protection will make a difference. Consider, for example, a simple case of a salvo attack against a single ship, and assume that the ship has passive protection that makes it possible to take two hits without any functional impairment. If the defense is perfect, the hit probability becomes zero—and we need no passive protection. But who can ensure a perfect defense in the future? If, on the other hand, the defense is not perfect and the hit probability for each missile becomes a not very high 20%, then the out-of-action probability for a combatant that has minimal passive protection becomes an appalling 60% when attacked by a salvo of four missiles, whereas for the two-hit ship it is near zero. Similar reductions are found for other salvo attacks.
Another way of expressing this benefit is to look at it from the attacker's point of view. For the attack to be effective many more missiles must be used against ships possessing sturdiness. Thus, for the above example the attacker need use only three missiles to get a 50% probability of knocking out the zero-hit ship, but he must use 12 missiles to accomplish the same against the two-hit ship. In other words, passive protection is a multiplier for the effectiveness of the defense. Especially for attacks on a group of ships it is obvious that the attacker quickly may have a problem, for he will have only a limited number of missiles that can be employed in each engagement.
The major benefits of passive protection are in saving lives, freeing some constraints on tactical choices, compensating for action mistakes or impairments of defensive capabilities, compensating for technical surprises, reducing material losses, helping to win engagements and wars, and ensuring dominance in the littorals by reducing or eliminating the chance of embarrassing losses of high-cost ships operating in "gray" situations of peacetime.
The Fleet after Next
The case for rebalancing the fleet to obtain ensured access and dominance in the littorals is convincing. Just what types and mixes of ships is not clear, for the future conditions over the next 20 or 30 years are difficult to predict. Future types could include Streetfighters, recognizing that their proposed small size would have both advantages and disadvantages. Their size could make it necessary to limit their functions, such as Sweden is doing with some of their proposed Visby-class coastal corvettes. Small ships also cannot carry passive protection that is effective against missiles, and if they were hit they would in all probability be put out of action or lost. Future uncertainty, coupled with the prevailing low tolerance for losses, means that other combatant types should be considered to cover all bets. These should be sturdy ships bigger than the Streetfighters, and more costly, but they could be made more capable as well. These large ships would attract more fire—because they would be easier to find, easier to hit, and more valuable targets. If used together with stealthy Streetfighters they may attract all the fire. All high-value combatants should have effective passive protection to ensure against embarrassing losses if they are used in the littorals.
Incorporating combatants with sturdiness for missile warfare should be one of the goals for the "fleet after next." But reaching this goal will require a change in attitudes and policies concerning passive protection. In view of the potential benefits, the subject deserves more attention. It should not be considered a problem for engineers to fit in, if we can afford it. The question of sturdiness of future combatants should be decided in the context of the selection of the best combatant types for future missions.
Mr. Hansen is a physicist and structural engineer, retired after 37 years service with the Naval Surface Warfare Center, Carderock Division, where he was head of the Protection and Weapons Effects Department. He presently is a consultant working through T. Carroll Associates, Engineers.
1. Vice Admiral A. K. Cebrowski, USN, and Captain Wayne P. Hughes, Jr., USN (Ret.), "Rebalancing the Fleet," pp. 31-34, Admiral Jay L. Johnson, USN, "Numbers Do Matter," November 1999, p. 32; Captain Wayne P. Hughes, Jr., USN (Ret.), "22 Questions for Streetfighter," February 2000, pp. 46-49; Rear Admiral Rodney P. Rempt, USN, "We're in the Enemy's Backyard," July 1999, pp. 43-46; John Lillard, "Austerity Is Not Affordable," August 1999, U.S. Naval Institute Proceedings, pp. 38-44; Lieutenant John C. Schulte, "An Analysis of the Historical Effectiveness of Anti-Ship Cruise Missiles in Littoral Warfare," Master's thesis, Naval Postgraduate School, 1994. back to article