The Lexington-class aircraft carriers were a pair of aircraft carriers built for the United States Navy (USN) during the 1920s, the and . The ships were built on hulls originally laid down as battlecruisers after World War I, but under the Washington Naval Treaty of 1922, all U.S. battleship and battlecruiser construction was cancelled. The Treaty, however, allowed two of the unfinished ships to be converted to carriers. They were the first operational aircraft carriers in the USN and were used to develop carrier aviation tactics and procedures before World War II in a series of annual exercises.

They proved extremely successful as carriers and experience with the Lexington class convinced the Navy of the value of large carriers. They were the largest aircraft carriers in the USN until the s were completed beginning in 1945. The ships served in World War II, seeing action in many battles. Although Lexington was sunk in the first carrier battle in history (the Battle of the Coral Sea) in 1942, Saratoga served throughout the war, despite being torpedoed twice, notably participating in the Battle of the Eastern Solomons in mid-1942 where her aircraft sank the Japanese light carrier . She supported Allied operations in the Indian Ocean and South West Pacific Areas until she became a training ship at the end of 1944. Saratoga returned to combat to protect American forces during the Battle of Iwo Jima in early 1945, but was badly damaged by kamikazes. The continued growth in the size and weight of carrier aircraft made her obsolete by the end of the war. In mid-1946, the ship was purposefully sunk during nuclear weapon tests in Operation Crossroads.

Development

The Lexington-class ships were originally designed to be battlecruisers, with heavy guns, high speed, and moderate armor protection. The Navy laid down six ships of the class in 1919–20. The terms of the Washington Naval Treaty of 1922 called for the scrapping of all capital ships then under construction, except that each signatory was allowed to designate two of the unfinished ships for completion as carriers. Globally, candidates for conversion included ships of the United States Lexington class, Japan's , and Great Britain's G3 battlecruisers.See: Washington Naval Treaty, Chapter II, Part III, Section II Lexington and Saratoga were selected by the United States because they were the farthest along of the six ships under construction.Stern, pp. 27–30

One major challenge the Navy's Bureau of Construction and Repair faced was the tonnage cap set by the treaty. Generally, under the treaty carriers were to displace no more than 27,000 tons. An exception, proposed by Assistant Secretary of the Navy Theodore Roosevelt Jr. and added to the treaty, allowed each signatory to convert two capital ships under construction into carriers displacing up to 33,000 tons.See: Washington Naval Treaty, Chapter I, Article IX But this was still not enough to cover the two Lexington conversions, which were expected to displace nearly 36,000 tons each. One solution would have been to fall back on a power plant that produced only half the desired power, which would have cost them c. 7 knots in speed, something the department found absolutely unacceptable. The alternative was to get creative: there was a clause in the treaty that offered a potential, if questionable, way out of this situation. The clause (Chapter II, Part III, Section I, (d)) read:

The intention was apparently that this was extra weight be applied some time in the future, during a mid-life reconstruction of the ship; but the American interpretation--that the extra weight could be applied to a modification during the original build-- was ultimately not challenged.

Conversion became a series of compromises and mixed blessings which would not have arisen had they been "specifically designed carriers" from the outset. On the plus side, the ships would have better anti-torpedo protection, larger magazines for aircraft bombs and, with the aft elevator farther forward than on the parallel design for a purpose-built carrier, more room for aircraft landings. On the minus side, a converted battlecruiser would be slower than a specifically designed carrier, have 16 percent less hangar space, less emergency fuel and, with "narrower lines" aft, not as wide a runway for an approaching airplane to aim at. Costs were similar: estimated cost for a brand-new carrier was estimated at $27.1 million, while conversion of a Lexington class hull would cost $22.4 million, plus the $6.7 million already sunk into them. Added together, the figure rose to $29.1 million.Friedman, p. 43Both of these figures (the $6.7 and $22.4) are estimates for one of the lesser-advanced ships like Ranger. The former cost would be higher and the second lower for one of the more-advanced ships.

Design and description

General description The ships had an overall length of , a beam of , and a draft of at deep load. Saratoga had a standard displacement of , and at deep load.Friedman, p. 390

One of their innovative features was a relatively new kind of bow called the bulbous bow or Taylor bow, named after its inventor, Rear Admiral David W. Taylor, who served as Chief Constructor for the U.S. Navy's Bureau of Construction and Repair in World War I. The result of a series of towing tests begun in 1910, this bow reduced water resistance by an average of six percent at high speeds, supported the forecastle and reduced bending stress on the hull. A disadvantage was the formation of a thick layer of water, part of the bow wave, which would creep up along the forward side of the hull at higher speeds, although this could be reduced to some degree by careful design of this area.Breyer, p. 235

Flight deck arrangements These ships were given an teak flight deck.The hangar was long; its width, constrained by the bulky funnel uptakes and boat recessess, varied from , and it had a clear height of 20 feet (6.1 m). Unlike most American carriers, it had no supplemental stowage space above the clear height, as the uppermost reaches of the hangar space were entirely taken up by a gallery deck, within which the crew was housed. The hangar floor had a surface area of , making it the largest enclosed space afloat, civilian or military, when built.Anderson and Baker, p. 310 Aircraft repair shops, 108 feet (32.9 m) long, were located aft of the hangar, and stowage space for disassembled aircraft was located in a 128-foot (39-m) long compartment beneath the hangar floor. The hangar was divided by a single fire curtain just forward of the aft aircraft elevator.

The carriers were fitted with two hydraulically powered elevators on their centerline. The forward elevator measured 30 feet (front to back) by 60 feet (side to side; 9.1 by 18.3 m) and had a capacity of , moving at a speed of 2 feet (0.61 m) per second when lifting a 12,000-lb (5.45-tonne) load. A section of the flight deck adjoining the rear edge of the elevator could split down the centerline to allow the tail of a long aircraft to pass through. aircraft otherwise too long. The aft elevator measured and could lift only 6,000 lb (2.7 tonnes). Munitions were delivered from the magazines by two hydraulically powered bomb lifts and one torpedo lift. A folding crane with a capacity of was positioned on the flight deck forward of the gun turrets. Aviation gasoline was stored in eight compartments of the torpedo protection system and their capacity has been quoted as either or .Anderson and Baker, p. 311 A flywheel-powered aircraft catapult, long, was fitted at the bow; it could launch a aircraft at a speed of . It was removed in 1934 as it proved to be unnecessary.

The Lexington-class ships were designed to carry 78 aircraft of various types, including 36 bombers,Anderson & Baker, pp. 310–11 but these numbers increased once the Navy adopted the practice of tying up spare aircraft in the unused spaces at the top of the hangar.Stern, p. 109 In 1936, her air group consisted of 18 Grumman F2F-1 and 18 Boeing F4B-4 fighters, plus an additional nine F2Fs in reserve. Offensive punch was provided by 20 Vought SBU Corsair dive bombers with 10 spare aircraft and 18 Great Lakes BG heavy dive bomber aircraft with nine spares. Miscellaneous aircraft included two Grumman JF Duck amphibians, plus one in reserve, and three active and one spare Vought O2U Corsair observation aircraft. This amounted to 79 aircraft, plus 30 spares.

In early December 1941, Lexington was ferrying 18 U.S. Marine Corps (USMC) Vought SB2U Vindicator dive bombers to Midway Atoll and at that time she embarked 65 of her own aircraft, including 17 Brewster F2A Buffalo fighters. During the Wake Island relief expedition later that month, Saratogas air group consisted of 13 Grumman F4F Wildcat fighters, 42 Douglas SBD Dauntless dive bombers, and 11 Douglas TBD Devastator torpedo bombers. The ship also carried 14 Marine Corps Buffalos for delivery at Wake.Lundstrom 2005, pp. 8–9, 35 Before the Battle of the Eastern Solomons in mid-1942, Saratogas air group consisted of 90 aircraft, comprising 37 Wildcats, 37 Dauntlesses and 16 Grumman TBF Avenger torpedo bombers.Lundstrom 1994, p. 21 In early 1945, the ship carried 53 Grumman F6F Hellcat fighters and 17 Avengers.Polmar & Genda, pp. 459–60

Propulsion Turbo-electric propulsion had been chosen for the battlecruisers because American companies struggled to produce the very large geared turbines necessary for such big ships and was retained when they were converted into aircraft carriers. One advantage of turbo-electric drive was that the substitution of flexible electric cables for bulky steam-lines allowed the motors to be mounted farther aft; this reduced vibration and weight by shortening the propeller shafts. Another was the ability to go astern at full power without needing a separate reverse turbine to do so, simply by reversing the electrical polarity of the motors. Other benefits were the ability to operate all four propellers if one of the turbo generators failed, and the possibility of operating only some of the generators at low speed with suitably higher loading and greater efficiency.Breyer, p. 218 "[Turbo-electric drive] was efficient, rugged and always reliable. But it was also heavy, intricate, and not easy to maintain and keep tuned up."Anderson and Baker, p. 312 The machinery also required special ventilation measures to dissipate heat and to keep out any salt air.W. McClelland, quoted in Anderson and Baker, p. 327 Even with this and elaborate insulation measures, protection from moisture or from flooding due to battle damage or other causes remained problematic and it posed the danger of high voltage to the crew if damaged.

Each propeller was in diameter and each of the four propeller shafts was powered by two electric motors acting in tandem. These motors were about five times the size of any earlier electric motor. Four General Electric turbo generators powered each propeller shaft and each was rated at , 5000 volts and 4620 amps of direct current (DC). Each of the four alternating current (AC) alternators produced 40,000 kVA. Sixteen water-tube boilers, each in their own individual compartment, provided steam for the generators at a working pressure of and a temperature of . The turbo-electric machinery of the Lexington-class ships was designed to produce a total of and propel the ships at , but each ship reached over and in sea trials in 1928. Six DC turbo generators were installed in the upper levels of the two main turbine compartments.

The ships carried a maximum of of fuel oil, but only of that was usable as the rest had to be retained as ballast in the port fuel tanks to offset the weight of the island and main guns. They demonstrated a range of at a speed of with of oil.Anderson and Baker, p. 313

Armament