It has been a little over half a century since the first nuclear-powered warship, the submarine USS Nautilus, signaled that she was under way on nuclear power in 1955. Carriers like George H.W. Bush are among the main beneficiaries of the naval revolution she represented. Nuclear power can drive such a ship at full speed for years on end. It provides the sort of electric power needed for modern electronics and, in the next carrier generation, for new devices like electric catapults and, possibly, lasers for self-defense. As a side benefit, a nuclear carrier does not suffer from the sort of smoke corrosion that used to destroy carrier radars and other electronics, not to mention carrier aircraft themselves.

The U.S. Navy’s journey to nuclear power began in 1946, when two scientists at the Office of Naval Research (ONR) pointed out that a submarine so powered would have unlimited underwater endurance at high speed. There was intense interest in high underwater speed because the Germans had pioneered it during World War II. The batteries which then powered submarines offered about an hour or less of endurance at maximum speed. The Germans had partly developed a closed-cycle Walter power plant that promised 10 hours at high speed. Nothing more seemed possible because a submerged submarine had no access to air for her diesel. The Germans had pioneered the snorkel, through which the diesel could breathe when the submarine was at periscope depth, but a submarine could not operate at maximum speed when snorkeling, and no submariner wanted to be limited to periscope depth.

The first nuclear powered aircraft carrier, USS Enterprise (then designated CVAN 65) cruises in the Gulf of Tonkin off the shores of Vietnam on May 28, 1966. Visible are A-4C Skyhawks (mostly parked on the bow). Four F-4B Phantom II fighters are parked next to the island, another one on the aft port flight deck. Next to the island two RA-5C Vigilante reconaissance planes are visible. The large radome belongs to an E-1B Tracer AEW aircraft. The tail of an A-3B Skywarrior bomber is barely visible behind the island. While Enterprise was a great achievement, she was the only ship of her class, lessons from her construction and operations being incorporated in the Nimitz class carriers that followed. National Archives photo.

At that time the only reactors in the world were used to make plutonium for atomic bombs. It was widely expected that atomic reactors would soon produce plentiful electric power, but that was a dream rather than a reality. Much of the enormous industrial team assembled to build the wartime atomic bombs (and the plutonium-making reactors) had dispersed, and the wartime bomb program run down to the point where, in 1946, the United States had no usable atomic weapons at all. Submariners were interested in new kinds of propulsion, but that generally meant various forms of closed-cycle engines, like the semi-developed German Walter plant. Surely it would be decades before nuclear power reached any sort of potential. The Bureau of Ships formed a small nuclear propulsion team, headed by Capt. Hyman Rickover.

Rickover sponsored studies of various alternative power reactors from which heat might be extracted in the form of hot water or molten metal or gas. Rickover’s decisive contribution was to realize as early as 1948 that he knew enough to build a prototype power plant. That was very courageous. Money was tight, and further studies might easily have uncovered some unsuspected problem. Indeed, Rickover initially bet on liquid metal, and only later switched his main focus to water. However, his decision led to the construction of a prototype plant. Rickover further accelerated development by deciding that the land-based prototype would be matched by the prototype planned for installation in the first nuclear submarine. Changes to the prototype to solve problems as they were encountered would be duplicated in the submarine reactor. By 1950, the Bureau of Ships was designing the prototype submarine. Rickover contributed further by demanding that it be armed, as a combatant, rather than limited to power plant tests. There was already interest in arming such a submarine with guided missiles, but Rickover wanted to separate the test of the power plant from the tests of such new weapons.

Rickover’s program was viable despite tight defense funds because major companies like Westinghouse and General Electric saw it as an opening into a potentially huge civilian power market. In 1948, Rickover attended a Submarine Officers’ Conference in Washington that discussed progress in the new power plants. Captains in charge of various programs complained that companies would not assign their best engineers, because it seemed unlikely that the navy would ever build many such plants, and because they had no civilian applications. Then Rickover spoke. He had no such problems. The companies were building the necessary laboratories at their own expense. They were pushing their best people into the nuclear program. It turned out that his plant was ready years before any of the others – and it was inherently far superior, because the closed-cycle plants offered only a few hours underwater at high speed. Even in 1952, he offered weeks, and that soon extended to months and then years before a submarine had to be refueled.

Rickover was interested in the potential of nuclear power throughout the navy. His whole career had been built in naval propulsion machinery, and he had witnessed several major U.S. advances, leading up to the remarkably efficient and reliable high-pressure high-temperature power plants of World War II. Their technology had given the wartime navy unprecedented mobility. One lesson was that new power plant technology had to be spread across the fleet if it was to offer its full potential. For example, a nuclear fleet would gain high-speed mobility, which would protect it from submarine attack (in a pre-nuclear submarine era). It would not be tied to tankers, which themselves might be attacked by an enemy. Once he felt he understood nuclear engineering, he proposed design of a range of larger and smaller plants. The smaller ones might be used to build less expensive submarines. The largest were clearly intended for carriers and cruisers. Chief of Naval Operations Adm. Robert Carney approved Rickover’s program in 1954, before the prototype Nautilus went to sea. The high end of the series of reactors offered 30,000 horsepower, twice what the Nautilus plant put out. The new Forrestal-class carriers required 280,000, so eight of the high-end reactors could power a carrier, particularly if their power could be boosted slightly.

A catapult crewmember communicates with flight deck personnel while preparing an EA-6B Prowler assigned to the Yellowjackets of Tactical Electronic Warfare Squadron One Three Eight (VAQ-138) for a steam catapult launch aboard the USS Carl Vinson (CVN 70). Nuclear power provides the steam today for catapults, and will provide the massive electrical power needed for electronic catapults and arresting systems, as well as radar and weapon systems, in the next generation of U.S. Navy carriers. U.S. Navy Photo by Photographer's Mate Airman Chris M. Valdez.

Preliminary design work on a nuclear carrier began in 1955; USS Enterprise was included in the FY 58 program, for the year beginning 1 July 1957.  She was a spectacular achievement, but she was also spectacularly expensive to build and to maintain. Each of her eight reactors required its own operators, for example. The hull large enough to accommodate this power plant was far more massive than that of a pre-nuclear carrier. Rickover argued vigorously that all future carriers should be nuclear, but the sheer cost of the new ship was a deterrent. After one more (non-nuclear) carrier, construction of new carriers paused for a few years (it had been running one per year) when money was diverted to the crash program to build Polaris strategic submarines – another type of warship which Rickover’s new kind of propulsion had made practicable.

Meanwhile Rickover’s Naval Nuclear Reactor organization strove to simplify carrier power plants. It realized that the key was cutting the number of reactors. It proved possible almost to double reactor power, so that a carrier could be built with four rather than eight, albeit with less power than Enterprise. This ship was not built. Secretary of Defense Robert S. McNamara argued that it would still be so much more expensive than a conventional carrier as not to be worthwhile. Rickover and other nuclear supporters argued that was an illusion. The nuclear carrier would be far less vulnerable, thanks to her sustained speed, she would need far less tanker support (she would still need fuel for her aircraft), and she would be easier to maintain. McNamara’s decision was embodied in USS John F. Kennedy, the last U.S. non-nuclear carrier. Echoes of McNamara’s arguments could still be heard in the 1980s, in attempts to eliminate nuclear power so as to cut carrier cost. The issue was generally the purchase cost of the carrier as compared with the cost of operating her over her lifetime. At the time it was probably not imagined that the U.S. Navy would typically operate carriers for as long as fifty years, far beyond the operating lifetimes of earlier kinds of warships. That was possible partly because the sheer size of these ships limits the stress imposed by the sea.

Compared to a steam plant, a nuclear plant requires a larger cadre of more skilled operators. Rickover was acutely aware that any nuclear accident would kill nuclear power for the U.S. Navy, so he insisted on high (some would say extravagantly severe) standards for those operating the plants and commanding the ships they powered. Experience suggested that for a small ship, a cruiser or a large destroyer, nuclear power entailed too high a cost in personnel. That cost was well worth paying in a submarine. A carrier and her air wing require so many highly skilled personnel that the additional cost of a nuclear power plant was bearable. If, as advocates of energy independence and conservation suggest, nuclear power will have a larger role in the future, the naval nuclear program will provide most of the new reactor operators needed. The Navy will have to compete with a livelier civilian sector, and the cost of nuclear personnel will undoubtedly rise. So, perhaps, will the cost of reactors, if the companies making them have a larger civilian role. Even in the 1950s operators were seen as a major nuclear expense, because they required so much specialized training.

Thus Naval Reactors continued to develop larger reactors that would need fewer operators. By the 1960s the U.S. Navy had not only a nuclear cruiser (Long Beach) but even a large nuclear destroyer (Bainbridge, later redesignated a cruiser). Each had two reactors. The U.S. Navy was then planning a class of Typhon missile destroyers with huge radars, which, it seemed, would need nuclear power to drive them. Naval Reactors developed a single reactor that could replace the usual pair of destroyer reactors. It never entered service, but the lessons learned made it possible for Naval Reactors to double power again (and then some) into a reactor two of which could power a carrier. This new reactor was available when Secretary McNamara left office (1967) and the design of another new carrier began – USS Nimitz.

Two F-14 Tomcats assigned to the Swordsmen of Fighter Squadron Three Two (VF-32) fly over the guided missile cruiser USS San Jacinto (CG 56) during an under way replenishment (UNREP) with the USS Harry S Truman (CVN 75). Nuclear powered carriers can devote their aviation fuel supply entirely to their air wing and escorts. U.S. Navy photo by Photographer's Mate 2nd Class H. Dwain Willis.

This was remarkable progress. It was little more than a decade since Rickover had received authority to develop his range of reactors. Now his organization was offering one about four times as powerful – not to mention much more fuel-efficient.

Enterprise was difficult to maintain because her eight reactors were closely coupled together. Like any other nuclear ship, she had to be opened up periodically so that the reactors could be refueled. In a carrier the power plant is buried deep in the ship, beneath the flight and hangar decks. These decks have to be cut open to give access to the reactors; there is no way to get at the vertical fuel rods from the side. That is why other modifications to a carrier are generally held back to refueling time. Alternatively, it might be said that much of the cost of operating a nuclear ship is spent when she is refueled. Eight closely coupled reactors required a huge refueling hole and an enormous amount of special piping.

Moreover, concentrating a ship’s power plant in one place makes her vulnerable to a single underwater hit. Since before World War II, U.S. design practice had been to split power plants so that no single hit amidships could immobilize a ship. Enterprise violated that requirement because of the need to concentrate those eight reactors (they shared important auxiliary machinery). With their single funnels, conventional carriers did suffer from some concentration, but they still had dispersed power plants. Since they needed no funnels, reactor plants could, at least in theory, be spread out more widely than their conventional predecessors, giving their ships better survivability.

Nimitz embodied that potential. Each of her two quite separate reactors drives a pair of steam turbines. Physically separating the reactors made it possible to disperse other vital parts of the ship, such as magazines. The split power plant is less vulnerable to attack or to other damage. It is also much easier to open up the ship to refuel two widely separated reactors. George H.W. Bush, the U.S. Navy’s newest carrier, has much the same reactor arrangement as Nimitz, but Naval Reactors has been working hard over the intervening forty years.

USS Nimitz (CVN 68) and Carrier Air Wing Eleven (CVW-11) carry out flight operations in support of Operation Iraqi Freedom. Nimitz was first of class for the generation of U.S. Navy nuclear powered carriers now in service. U.S. Navy photo by Photographer’s Mate 3rd Class Kristi Earl.

Since Nimitz, Naval Reactors has sought to lengthen the interval between fuelings, because that cuts the cost of running a nuclear ship. This is a matter of the design of the reactor’s nuclear core (new cores are designed to fit existing reactors, so in effect all nuclear carriers are upgraded over time). A reactor does not simply run out of fuel; when it is shut down there is still a good deal of burnable uranium in the fuel rods. Instead, as the fuel is used, byproducts such as Xenon form in the rods. Xenon in particular can poison the reactor, because it absorbs the neutrons that drive the chain reaction powering it. Changes in core design make it possible to run longer before the rods must be removed and the material inside purged of Xenon. Once enough Xenon has been formed, the reactor has to shut down. The Xenon poisoning problem recalls the very old problem of ships burning coal: periodically they had to turn down their boilers so that the ashes choking them could be removed. The difference is that Xenon cannot simply be sloughed off and the reactor restarted. It has to be chemically extracted from fuel rods along with other byproducts of nuclear fission (new rods are inserted into the reactor at refueling time). The time scale is of course far longer now. The goal is a core that lasts the life of the ship, so that she is never refueled. That is being done for submarines. Current cores last 20 to 25 years, limiting a carrier to one refueling during her career. The next carrier, USS Gerald R. Ford, is to have a full-life (50 year) core. Her reactors are also to be about a quarter more powerful than those of George H.W. Bush.

Rickover envisaged an all-nuclear task force with unlimited endurance. For a time, in the 1970s, there was a legal requirement that all U.S. combatants of over 8,000 tons be nuclear-powered, unless the president specifically waived that condition. The U.S. Navy built several large nuclear destroyers (later designated cruisers), but found them unsatisfactory. In contrast to a carrier, the nuclear power plant was too great a fraction of their building and operating cost. They proved cramped, and they lacked anti-submarine capability (they were too noisy, because it would have been too expensive to silence their power plants).

Moreover, a carrier battle group cannot be completely independent of tankers. Naval aviation is a very demanding profession. Even when a carrier is not fighting, her pilots must keep flying to maintain their proficiency. The carrier must take on aviation fuel periodically. Her gas turbine-powered escorts burn the same fuel, so it is not so very difficult for the carrier to fuel them periodically. The carrier herself benefits hugely from her nuclear power plant. It turns out that carriers need layers of liquids in their sides as torpedo protection; in non-nuclear days they carried the ship’s fuel oil. Eliminating the need for the carrier’s own fuel left the layers of fuel for her aircraft (which gained more flying days between refueling) and for the escorts. This compromise has proven quite successful.

This article was first published under the title “Under way on Nuclear Power” in Freedom at Work: USS George H.W. Bush CVN 77.

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