The design challenges the Navy's Bureau of Construction and Repair (C&R) faced with this class were considerable, as the combined requirements of optimum hitting power, extreme speed and adequate protection taxed the knowledge of its naval architects and the technology of the time.

To do so with a capital ship required a hull and a power plant of unprecedented size for a U.S. naval vessel and careful planning on the part of its designers to ensure it would have enough longitudinal strength to withstand bending forces underway and the added stresses on its structure associated with combat.

Even so, it took years between initial and final designs for engine and boiler technology to provide a plant of sufficient power that was also compact enough to allow a practical degree of protection, even in such large ships.

While four of the ships were eventually canceled and scrapped on their building ways in 1922 to comply with the Washington Naval Treaty, two (Lexington and Saratoga) were converted into the United States' first fleet carriers.

[2][A 2] Both saw extensive action in World War II, with Lexington conducting a number of raids before being sunk during the Battle of the Coral Sea and Saratoga serving in multiple campaigns in the Pacific and the Indian Ocean.

[A 3] As early as 1903, questions arose in the Naval War College (NWC)[4] about the overall effectiveness of large armored cruisers such as the Pennsylvania- and Tennessee-class vessels just then coming into service.

The NWC's 1903 annual summer conference report, which included a staff memorandum on all-big-gun capital ships, also suggested a new type of cruiser that would be armed and armored much like a battleship.

[6] As the NWC continued its studies, the Imperial Japanese Navy (IJN) scored a decisive victory over the Russian Baltic Fleet at the Battle of Tsushima in 1905.

Strategist and Admiral Alfred Thayer Mahan had warned then-Assistant Secretary of the Navy Theodore Roosevelt in 1897 of a much greater likelihood of conflict in the Pacific than in the Atlantic.

The following day, the Secretary of the Navy asked the General Board to consider the construction of American battlecruisers for Pacific service, as the Pennsylvanias and Tennessees would no longer be viable units in the face of such opposition.

[15] The six Lexington-class ships were named Lexington, Constellation, Saratoga, Ranger, Constitution, and United States and were designated CC-1 through CC-6,[A 5] with "CC" signifying their status as battlecruisers.

HMS Renown had to go into drydock immediately following her preliminary gunnery tests because the hull structure could not withstand the bending stresses from firing her forward main guns.

When the "large light cruiser" HMS Courageous weathered a heavy gale during her initial trial run, a number of her outer hull plates were so distorted that they had to be removed, sent back to the foundry and renewed.

[20] In the Lexingtons longitudinal strength was challenged further by the large amount of freeboard required at the forward section of the hull to keep the ships dry and maintain a high speed in various types of weather.

These factors plus the ships' unusual length prompted Naval Constructor R. H. Robinson, who led the design group for the Lexingtons, to make careful analyses of strength, buoyancy and stresses expected in service.

Large numbers of anti-submarine warfare vessels and merchant ships were needed to ensure the safe passage of men and materiel to Europe during Germany's U-boat campaign and were given top priority.

This opened the opportunity for a massive redesign, the need for which had become apparent in light of experience gained in the Battle of Jutland, fought shortly after the initial design for the Lexingtons had been approved and in which three British battlecruisers had been lost.

Other factors for this decision were the discovery of plans by Britain and Japan for new battlecruisers armed with 15-inch (381 mm) and 16-inch guns (respectively) and the recommendation of the Bureau of Ordnance to give these ships the ability "to inflict fatal damage on the enemy's most powerful vessels at a distance no less than that at which she can be reached by the heavy gunfire of these opponent battleships."

On 8 April 1918, he told the Lexington design staff to plan a vessel combining the principal features of battleship and battlecruiser so that it would have the maximum possible speed, main armament and protection.

Other changes included a widening of the ship to allow for an adequate torpedo protection system and an increase in vertical belt armor to 7 inches (180 mm).

[26][28][29] Four proposed redesigns were submitted to the General Board on 3 June 1918, along with a letter that requested a formal reconsideration by the Navy that the Lexingtons be armored to protect them only against fire of guns six inches and smaller.

Commander in Chief in European waters, Admiral William S. Sims, to argue for the redesigned vessels by pointing out that Hood had already brought about the very revolution that the Board wished to suppress.

[Note 3] Debate continued while the project remained suspended until May 1919, when the Board decided that the battlecruisers should be built as planned, except for a slightly slower version of Design B from C&R with increased protection for turrets, conning towers, magazines and communications.

[31] Turbo-electric propulsion was selected for the battlecruisers despite the fact it needed more room than geared turbines to allow for better underwater protection that wartime experience showed was essential.

The substitution of flexible electric cables for bulky steam-lines meant that the motors could be mounted further to the rear of the ship, which reduced both vibration and weight by shortening the propeller shafts.

[34] Four General Electric turbo generators powered each propeller shaft and each was rated at 35,200 kilowatts (47,200 hp), 5000 volts and 4620 amps of direct current (DC).

[36] The guns were capable of firing a 1,400 pounds (640 kg) armor-piercing (AP) projectile at a muzzle velocity of 2,800 fps (853 m/s) to a range of 24,000 yards (22 km) at a maximum angle of 15 degrees.

Under the terms of the treaty, any capital ships that were under construction by the five signatories (the United States, Great Britain, France, Italy and Japan) had to be canceled and scrapped.

[2] The clause (Chapter II, Part III, Section I, (d)): No retained capital ships or aircraft carriers shall be reconstructed except for the purpose of providing means of defense against air and submarine attack, and subject to the following rules: The Contracting Powers may, for that purpose, equip existing tonnage with bulge or blister or anti-air attack deck protection, providing the increase of displacement thus effected does not exceed 3,000 tons (3,048 metric tons) displacement for each ship.

Two of the battlecruiser hulls were reordered as the Lexington-class aircraft carriers Lexington (CV-2) and Saratoga (CV-3) under the terms of the Treaty, while the other four ships were formally cancelled and scrapped in place.