Monday, December 1, 2014

The Lexington-class: America's Only Battlecruisers

      Of the major naval powers at the end of WWI the U.S was the only power not to have built battlecruisers. The British pioneered the concept in 1907 with the HMS Invincible and were quickly followed by the Germans with the SMS Von der Tann. At the beginning of the 20th century it was a recognized deficiency within the U.S. Navy that there were not enough cruisers to scout and support the main battle line. Beginning in the early 1910s the General Board began to develop designs for what a U.S. battlecruiser should look like. In 1916 Congress granted funding for a class of six battlecruisers, but due to WWI construction did not start until 1920 after the U.S. entry into WWI and a major redesign of the class using British experience from Jutland. Unfortunately, or perhaps fortunately, the Lexington-class was one of the classes of ships scraped after the ratification of the Washington Naval Treaty. Of the six ships planned only two were completed (both as aircraft carriers), the Lexington and Saratoga of WWII fame. However, the focus of this post is on the Lexington-class in it's original battlecruiser form.
      In the early 1900s the General Board wanted to enlarge the U.S. cruiser fleet to provide scouts for the battle line of the Navy. Congress was unwilling to provide funds for the requested cruisers, rather focusing on battleships. This forced destroyers to take up the slack in acting as the eyes of the U.S. battle line. In 1916 Congress finally gave it's approval for a class of six battlecruisers to be completed by 1920. This first design approved by Congress was to be armed with 10 14in guns, a displacement around 33,500 tons (this first design is comparable to the British Renown), a top speed of 35 knots, and very thin armor. Work was ceased on the design with the American entry into WWI  in November 1917 as all shipyard capacity was devoted to merchant vessels and ASW craft. With the U.S. entry into WWI Britain gave the U.S. access to their experience with battlecruisers, especially that gained from Jutland. The two redesigns of the Lexington-class from 1917 until 1919 turned the Lexington-class into what was essentially a fast battleship, combining the speed of a battlecruiser with the firepower of a battleship. Armament was increased to 8 16in guns, armor was increased which resulted in a drop in the class's top speed to 33 knots. This redesign was heavily influenced by the HMS Hood which the British viewed as a hybrid battleship and battlecruiser.
     The final design specifications of the Lexington-class are drawn from Norman Friedman's U.S. Cruisers: An Illustrated Design History and Siegfried Breyer's Battleships and Battlecruisers, 1905 to 1970.

Light ship
Deep load

Length (waterline)
850 feet
Length (overall)
874 feet
105 feet
Draft (light ship)
30 feet

Main battery
8 16”/50 Mark 2 guns
Secondary battery
16 6”/53 Mark 13 guns 
Anti-Aircraft battery
6 3”/50 Mark 10 guns
Torpedo Tubes
8 21” Tubes

Main side belt
7” tapering to 5” at the ends of the ship
Upper deck
1.25” to 2.25”
Upper armored deck
Lower armored deck

Shaft horsepower
180,000 SHP
Maximum speed
33.25 knots
Endurance @ 10 knots
10,000 miles

16"/50 Mark 2 outside the Washington Naval Yard in 1974
     The Lexington-class battlecruisers were to carry a main armament of eight 16"/50 Mark 2 guns in four twin turrets. Originally the Lexingtons were to be armed with 14 inch guns, but were upgunned due to the increasing caliber of naval guns worldwide and the longer range and better penetration of 16" guns. The Lexingtons were also to carry 16 6"/53 guns (10 in casemates and 4 in open air) to defend against destroyers. The anti-air armament consisted of 4 3"/50 guns at the time of the design, but by the time the ships were being built the number was upped to 8. Had the Lexingtons been built as planned it is likely that their casemate guns would have been removed and replaced at some point, and the guns mounted in the open would have been removed in the 1930s to make room for an increased AA armament. Their AA armament would have also been exponentially increased with everything from 0.50" MGs in the 30s to twin 5"/38 guns and 40mm Bofors cannons by WWII. To get an idea of the layout of the armament to be carried by the Lexington-class below is a sketch produced by the General Board in 1919 which was one of the later designs and extremely similar to the final design (I know there is an actual line drawing of the Lexingtons produced by the General Board in June of 1919, but the Navy does not seem to have it in their online archives).
(Click on the photo to enlarge)
     The armor scheme on the Lexingtons was influenced by the HMS Hood in that the main side belt was inclined outwards at 11.5 degrees to increase it's effective thickness against horizontal fire. The main side belt was to have a maximum thickness of 7 inches tapering to 5 inches at the ends of the ship. The cumulative deck protection was 3.75 inches split between the main deck, the protective deck, and the splinter deck. Turret armor was 11in on the face, 6in on the sides, and 5in on the roof of the turret. Comparatively, the Hood had a main side belt of 8in which thinned to 5-6in at the ends of the ship. Deck armor was 3in amidships, and 7in over the magazines.
     The top speed of the Lexington-class as designed was to be 33 knots. The Lexingtons would have had 16 Babcock boilers powering 4 GE turbines, each turbine driving one of four propellers. Total shaft horsepower of each Lexington was to be 180,000 SHP. This powerful machinery would later prove invaluable during the Lexington and Saratoga's days as carriers. To compare against a contemporary battlecruiser, the Hood had a top speed of 31 knots during trials, and that achieved by pushing her boilers beyond design specifications (the design SHP of the Hood was 144,000 but the speed of 31 knots was achieved with 151,280 SHP).
     While the Lexington-class was the only class of battlecruisers built (not commissioned) by the U.S. Navy, the Alaska-class have also been referred to as battecruisers in the last few decades in various books. However, the Lexington-class was designed explicitly to act as scouts for the main battle line of the Navy and to act as a fast squadron as part of the battle line itself. The Alaska-class was designed as a "cruiser-killer" meant to take on Japanese heavy cruisers, and escort carriers on operations independent of the Battle Force without detracting from the firepower of the Battle Force. The design requirements were different for the Lexingtons and the Alaskas. The Lexingtons were faster, better armored (relative to the Alaskas), and better armed than the Alaskas to carry out their mission of supporting the battle line. Whereas, the Alaskas were meant to operate apart from the Battle Line supporting carrier operations. Any comparison between the two class is wrong because they were designed for different mission sets.

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