Battlecruisers are a new class of capital warship which was developed by the Royal Navy in parallel with its introduction of dreadnought battleships. A direct evolutionary development of pre-dreadnought armored cruisers, they are designed to fulfill the same strategic role: a fast, powerful medium warship which can outrun a battleship and outgun all lesser warships. However, battlecruisers differ from their armored cruiser predecessors in being comparable in size and tonnage to contemporary battleships.
Historically, the U.S. Navy considered a variety of battlecruiser and dreadnought armored cruiser concepts as early as 1903, but did not commit to actual construction of any until the Lexington class battlecruisers of 1915. These would have been the largest and most powerful battlecruisers of their day, exceeding even the Royal Navy's famous HMS Hood, but construction was halted by World War I and subsequently canceled in accordance with the terms of the Washington Naval Treaty.
In this alternate timeline, the Lexingtons remain the only "official" battlecruisers constructed by the United States (and are still cancelled), but several new classes of dreadnought cruisers are fielded prior to World War I and again after the expiration of the Washington Naval Treaty. These warships are substantially larger and more powerful than pre-dreadnought armored cruisers, but the U.S. Navy continues to use the "armored cruiser" designation since they do not have capital-caliber guns.
Dreadnought Era
The U.S. Navy initially seeks to build eight to twelve new dreadnought armored cruisers to replace its pre-dreadnought armored cruiser force of two Maine class, six Pennsylvania class, and four Tennessee class. However, Congress is only willing to authorize six cruisers. The construction of these cruisers is spread out in a four-year cycle which is intended to both spread out their cost and to enable each new class to take advantage of operational experience from the previous class.
California Class (1905)
The California class armored cruisers are designed in parallel with the South Carolina class battleships as a cruiser version of the "all big gun" warship.
Design
The Californias have a standard displacement of 15,000 tons and measure 550 feet at the waterline with a beam of 75 feet and a draft of 25 feet.
Armament
The Californias are armed with a main battery of eight 10"⁄40 Mark 3 guns in four twin turrets and a secondary battery of twenty 3"⁄50 rapid-fire guns in superstructure casemates.
The main battery is arranged in a 2-A-2 configuration with superfiring pairs of turrets on the forward and aft centerline. These are the same guns and mountings previously used on the Tenneseee class armored cruisers, but with the #2 and #3 mountings raised by two decks to fire over the #1 and #4 mountings.
The secondary battery is placed with six casemates on each side of the 01 level superstructure and four casemates on each side of the 02 level superstructure.
Propulsion
In order to achieve the 25-knot speed necessary to maneuver "over" the 21-knot line of battle, the Californias are the first large American warships to adopt turbine machinery. Twelve coal-fired boilers provide superheated steam to high-pressure turbines driving two outboard propeller shafts and low-pressure steam turbines driving two inboard propeller shafts. Astern turbines for reverse operation are integrated into the same casings as the low pressure turbines. All turbines are of the Curtis (impulse) type, with the high-pressure turbines having two velocity-compounded stages followed by six simple stages, the low-pressure turbines having six simple stages, and the reverse turbines having two velocity-compounded stages.
Los Angeles Class (1909)
The Los Angeles class armored cruisers were initially intended to be improved repeats of the generally successful California class, but the design is heavily revised in response to the Royal Navy's Invincible class battlecruisers. While Congress is very reluctant to authorize such large and expensive armored cruisers in addition to all of the new dreadnought battleships being constructed, the large number of battlecruisers completed and under construction in Europe at this time presents a threat that must be answered.
Design
The Los Angeleses have a standard displacement of 17,000 tons and measure 550 feet at the waterline with a beam of 80 feet and a draft of 25 feet. Although there is considerable pressure to field a direct counterpart to the Invincibles, the USN strongly feels that a 10" armored cruiser with a larger number of main battery guns is a superior alternative to a 12" armed battlecruiser class of similar tonnage.
Armament
The Los Angeleses are armed with a main battery of twelve 10"⁄40 Mark 3 guns, a secondary battery of twelve 4"⁄50 Mark 9 guns, and a tertiary battery of four 3"50 Mark 5 guns.
The main battery is arranged in a 2-A-2 configuration with superfiring pairs of three-gun turrets on the forward and aft centerlines. Unlike the triple turrets for the contemporary New York class battleships, these are “three gun” turrets with the guns individually sleeved and independently elevating.
The secondary battery is arranged in four twin and four single pedestal mountings on the main deck. The twin mounts are placed forward and aft of the superstructure on each side, and the single mounts are placed amidships on each side. All of the mountings are protected by armored gun shields. The 4" twin pedestal mounting had been previously tested on destroyers with only limited success, but is much more effective on the cruisers as here it is paired with new ammunition lifts which can deliver shells to the gun crews at a high rate.
The tertiary battery is arranged in four single high-angle pedestal mountings placed one on each side of the forward deckhouse 03 level and one on each side of the aft deckhouse 02 level. This is considered to provide the best practical field of fire for air defense.
Propulsion
The Los Angeleses utilize direct drive turbine propulsion similar to that of the previous Californias, but with the addition of auxiliary cruising turbines for more efficient low-speed operation. Sixteen coal-fired boilers provide superheated steam to two high-pressure turbines and two low-pressure turbines. The cruising turbines are four relatively small reduction geared turbines which are connected to the shafts by disconnecting clutch mechanisms.
Phoenix Class (1913)
The Phoenix class armored cruisers are a further development of the Los Angeles class. Two were authorized in 1913 and four more in 1915, but the latter were put on hold due to the U.S. entry into World War I and subsequently cancelled.
Design
The Phoenixes have a standard displacement of 18,000 tons and measure 550 feet at the waterline with a beam of 80 feet and a draft of 25 feet. Although foreign battlecruisers are now on a clear path to follow “superdreadnought” battleships in embracing dramatically greater size and firepower, the U.S. Navy maintains the position that a fast armored cruiser with balanced armament and protection remains the superior design choice for a sub-capital warship. This is partly a polite fiction; a bigger reason is that Congress is only barely willing to fund the construction of significantly less expensive armored cruisers in addition to battleships.
Armament
The Phoenixes are armed with a main battery of twelve 10"⁄50 Mark 4 guns, a secondary battery of twelve 5"⁄51 Mark 8 guns, and a tertiary battery of four 3"50 Mark 5 anti-aircraft guns.
The main battery is arranged in a 2-A-2 configuration with a superfiring pair of three-gun turrets on the forward centerline and a superfiring pair of three-gun turrets on the aft centerline. In order to compete with the larger-calibre main guns being adopted by foreign battlecruisers, the new Mark 4 guns are designed with longer barrels and larger firing chambers to accomodate heavier propellant charges and thus achieve a substantially higher muzzle velocity of 2,900 FPS. This is coupled with new gun mountings with an increased maximum elevation of thirty degrees and a loading angle of ten degrees.
The secondary battery is arranged in four twin casemate mounts set into the forward and aft corners of the 01 level superstructure and four single casemates set into the sides of the 01 level superstructure.
The tertiary battery is arranged in four individual high-angle pedestal mountings placed one on each side of the forward deckhouse 03 level and one on each side of the aft deckhouse 02 level. This is considered to provide the best practical field of fire for air defense.
Propulsion
The Phoenixes are the second production class of warship ever fitted with turbo-electric propulsion, and are considered the most demanding test of the new technology since a fast armored cruiser requires machinery of the greatest power, reliability, and endurance. The propulsion plant consists of twelve boilers feeding superheated steam to three pairs of turbines, which turn six alternators powering eight electric motors for four propeller shafts.
The boilers are oil-fired water-tube units with integrated superheaters, producing dry steam at an operating pressure of 300 PSI and temperature of 460 F. The boilers and "steam side" supporting equipment (evaporators, condensers, etc) are installed in six boiler rooms which are paired port and starboard along the sides of the lower deck level. Steam from any boiler can be routed to any turbine set, although the norm is to rotate the boilers with six active at a time for economical cruise. The air intakes and boiler exhausts are trunked to three funnels, one for each pair of boiler rooms.
The turbines are three Curtis type (impulse) high-pressure turbines and three Parsons type (reaction) low-pressure turbines, with both types operating at a constant speed of 1,800 RPM. The turbines, generators and "electric side" supporting equipment are installed in three turbogenerator rooms which are located on the centerline between the pairs of boiler rooms. Each turbogenerator room contains a high-pressure and low-pressure turbine pair, two 450-volt AC main electrical alternators, and two 120-volt DC ship's service turbogenerators (SSTGs). Each turbine directly drives a single alternator, while the SSTGs incorporate their own small geared turbines and are fed steam in parallel to the main turbines.
The electric motors are of the externally excited, synchronous AC type and produce 5,000 equivalent horsepower each at 240 RPM; they were the largest electric motors in the world until eclipsed by the 22,500 equivalent horsepower motors developed for the Lexington class battlecruisers. Two motors were fitted on each propeller shaft, with the motors for both inboard shafts in a shared centerline motor room and the motors for the outboard shafts in individual port and starboard motor rooms.
San Francisco Class (1917)
Four San Franscisco class armored cruisers were authorized in 1917, but construction was suspended due to World War I and then cancelled due to the Washington Naval Treaty.