Saturday, December 31, 2011

Aircraft Carriers

Operational Limits

The hull dimensions of the first post-war USN carrier design were tightly constrained. Draft was limited by the water depth at the graving dock used for construction. Both the waterline beam and the waterline length were also limited by the graving dock dimensions. The limited beam determined the maximum possible hull depth. Speed was primarily impacted by the displacement, waterline length and the available power. Because speed was a firm requirement, and the length and propulsive power were both limited, the displacement was also constrained. Therefore, the internal volume and available deck area of the first new post war Forestal class carriers could not be significantly increased. These dimensional constraints remained valid for the two-decade later Nimitz class carrier design. But, the nuclear propulsion plant of the Nimitz class provided slightly more propulsive power and its required speed was a little slower; so, its hull could be a little fuller. Both the length and the beam of the Nimitz class were also inconsequentially increased. The higher displacement Nimitz class was, therefore, functionally similar to earlier conventional carriers, except that the conventional steam plant was replaced by nuclear reactors.

Because of its limited deck area, the Nimitz class could not meet later USN habitability standards, which had to be waived. Consequently, USN volunteer sailors had to live in austere conditions like their conscripted predecessors had in the 1950s. Moreover, due to design constraints, enlisted personnel had to be grouped in huge impersonal berthing compartments that provided no privacy or territoriality. This remains true today.

The Nimitz class was originally designed to support maintenance-demanding 1960s aircraft. These aircraft could not be rapidly rotated to sustain a high sortie rate. Most were not capable of effective 24/7 continuous air-to-ground operations. So, the Nimitz class only had two watches of aircraft support personnel, as it was not expected to be capable of 24/7 sustained air operations. Because of limited hull volume and deck area, the loads of aviation consumables, i.e., spare parts, drop tanks, ammunition and fuel were all constrained. While the nuclear plant gave the Nimitz class an ability to continuously cruise at high speed, its conventionally-powered escorts, when operating at high speed, would have to be refueled every two days by tankers. During combat, its aircraft would run out of consumables in about 5 to 7 days. A Nimitz class carrier could only sustain continuous air operations if replenishment ships were always available.

Introduction of the reliable, digital F-18 with its advanced avionics meant that the Nimitz class carrier could be equipped with a multi-mission, reliable, 24/7 combat aircraft, capable of sustaining a high sortie rate. A practical airframe limit of about 7 to 8 limited-range 1.5 hour sorties per day per aircraft was technically achievable. Recent combat experience has consistently shown that air crew cannot generate more than about 2.5 sorties per day over sustained periods because air combat is just too physically and mentally exhausting. Therefore, achieving this sortie rate with only one pilot per aircraft would be impossible. Moreover, the provision of only two versus three watches of aircraft support personnel on the Nimitz class would have, in any event, constrained daily the sortie rate.

Post F-18 USN aircraft carrier operations were, therefore, generally based on groups of carriers operating together. With three available, two would operate 24/7 with the third resting and replenishing. With four available, two would operate at night and rest or replenish during the day time, with the other two operating on a reverse cycle. This operational concept amounted to virtual attrition. Nimitz class carriers were far less operationally capable than generally thought.

The Nimitz class was originally designed as a CVA attack carrier, with a virtually all fast-jet air wing of about 90 aircraft. During the cold war, as the USN mothballed its older converted Essex class anti-submarine carriers, the Nimitz class air wing was modified, and it was re-designated as a CV. Squadrons of anti-submarine aircraft and helicopters were added and the number of fighter attack fast-jets considerably reduced. Today, Nimitz class carriers carry four very small 12 plane F-18 squadrons, fewer fast-jets than they theoretically can. The multi-role F-18s are used for air attack, air defense and as tankers. Normally, the historical serviceability rate of deployed air wing F-18s is about 85%. Four of the F-18s would generally be fully allocated to the airborne tanker role. These are primarily used to extend the on-station time of CAPs and to provide fuel for returning aircraft that often have to make multiple landing attempts at sea. In wartime, carriers will always maintain at least one forward CAP for air defense. Additional aircraft, configured for the air defense mission are maintained on the flight deck for QRA launch. Thus, 8 to 16 serviceable aircraft are generally continuously allocated to self-defense. This means that a single carrier has only about 18 to 20 F-18s available for offensive operations. If two carriers are operating together while maintaining only one CAP station, the number of F-18s available for strike operations per carrier would increase to about 27 to 35. USN strike tactics are to configure a large portion of these offensive sorties for supporting missions such as air-to-air or SEAD. Thus USN Nimitz carriers can generate very few actual offensive strike missions daily. During Desert Storm, USN carriers generated fewer than 20 long-range bombing sorties per carrier per day.

Nimitz class carriers became further underutilized by their air wings when their fixed-wing S-3 ASW squadrons were disbanded. The USN could then have increased the size of its embarked F-18 squadrons, but it could not do this within current budget allocations. In retrospect, it is obvious that it would have been cost effective to increase F-18 squadron size from 12 to 16 aircraft while decommissioning two carriers and their air wings. This would have saved several billion dollars a year. But, it would have reduced the number of senior command billets at the Captain and Rear Admiral level which was then, and remains today, wholly unacceptable to the USN.

Over the last decades, the USN has conducted several surge exercises on its F-18 equipped CVs. A third watch of aircraft support personnel and a second set of air crew were temporarily added to existing carriers and their air wings. The results were predictable! The number of fast-jet sorties which could be generated daily roughly doubled. The enhanced carrier air wings could have sustained intense 24/7 operations for about 3 to 4 days until the available fuel, ordnance and other consumables were expended. Having conducted these illuminating operational tests, the USN then did nothing to implement the lessons learned.

Based on the results of the surge exercises and the known operational limits of current Nimitz class carriers, the USN could safely cut back the number of commissioned carriers from 11 to 7. Two additional unmanned carrier hulls would be in long-term overhaul in decommissioned status, thereby maximizing the availability of the 6 commissioned combat-ready carriers. There would be only 6 active air wings, each with four 16 versus 12 strong F-18 squadrons. The seventh carrier would only be used for the at-sea training of 4 new reserve air wing surge teams. Consequently, the seventh carrier would have only a partial ship’s crew and minimal air wing personnel. The 4 reserve air wing surge teams would each comprise sets of air crew plus aviation support teams. The personnel of the 4 reserve air wing surge teams would train on shared air frames organized into specialized non-deployable training units located on both coasts.

World-wide response times and regional wartime sortie generation capability would be the same as before, but the number of active personnel and the number of dedicated escorts and all associated operating costs would be very considerably reduced.


USN carriers were designed to defeat typical USN anti-ship weapons, which included torpedoes and high explosive (HE) and armor penetrating high explosive (APHE) bombs of varying sizes. Carrier magazines were provided with side and top ballistic protection designed to prevent penetration by the most severe of these threats in order to preclude catastrophic mass detonation. The explosion of the Battleship Arizona at Pearl Harbor was a classic case of mass detonation, which is the virtually simultaneous detonation of stored ammunition. Starting with the CVN-71, new construction Nimitz class carriers were also provided with limited protection against Soviet large diameter shaped charge (HEAT) missile warheads. This limited protection has reportedly been subsequently retrofitted into at least some earlier carriers.

Air delivered bombs have a sub-sonic impact velocity. This limits their ability to penetrate through moderate thickness ballistic armor protection. But more recent Soviet anti-ship missiles had very high super-sonic impact velocities. Their warheads, therefore, were the equivalent of World War II battle cruiser or battleship APHE shells. Because of their vastly higher kinetic energy at impact, these warheads have much high penetrability than sub-sonic bombs of similar weight. De-classified World War II armor protection data indicates that it would require at least 10 to 12 inches or more of conventional steel armor plate to defeat these advanced super-sonic APHE threats. Based on open source data, USN carrier designs employ much thinner steel armor. Moreover, the US can no longer produce thick ballistic steel armor. Consequently, it is very likely that the ballistic protection of all existing US carriers can be penetrated by these advanced threats. If it is assumed that the hit distribution of these weapons will be random, then the probability of any such weapon actually penetrating into a major magazine would probably be less than 10%. But, current state-of-art seeker technology is available which permits the use of selective aim points. This means that the probability of a weapon being specifically targeted against a major carrier magazine can be very high. Providing all-around protection for carrier ammunition magazines that would defeat both HEAT and super-sonic APHE warheads would require an increase in hull depth and volume and a significant increase in displacement. The increase in displacement would require a very expensive increase in propulsive power in order to maintain speed. Based on the characteristics of the latest USN carrier, now under construction, which are generally similar to the characteristics of the Nimitz class, it appears highly probable that this design is not protected against these advanced threats.

When the first nuclear carrier was being designed, Admiral Rickover unilaterally decided that a nuclear reactor was no different than a conventional steam boiler. Therefore, unlike magazines, the nuclear reactor compartments of carriers are not specially protected by increased boundary armor. A penetrating enemy weapon could, therefore, break containment and cause a massive uncontrollable nuclear leak. Even if the ship did not sink, it would be a radiated hulk which could not be repaired for decades. The reactor spaces are located immediately adjacent to large magazines cumulatively holding several thousand tons of ammunition. If there was a mass detonation in an adjacent magazine, the reactor compartments would, almost certainly, be ripped apart. If this were to occur in port or in shallow water, the environmental result would be absolutely catastrophic.

The vulnerability of USN aircraft carriers to advanced weapons was no secret to Soviet engineers. That’s why they developed weapons to exploit known carrier weaknesses. Yet, the USN has maintained tight control of information about the vulnerability of its carriers. This was done in order to neutralize the USN’s real enemies, first, the USAF, which would have used this information to fight internal battles within the Pentagon over funding and force levels, and, second, Congress, which has to authorize new construction and force levels.

I believe construction of all vulnerable nuclear powered carriers, beyond those already in service, should immediately be cancelled or converted to conventional power. In this age of terrorism, all foreign port visits by existing nuclear powered carriers should also be terminated. In order to survive, carriers have to stay well off shore and remain mobile, operating in deep water.

No comments:

Post a Comment