Alaska-class CBs: America's Cruiser-Killers

     The United States Navy has never officially completed any ships under the designation "battlecruiser". There was a class of battlecruiser constructed during the early 1920, the Lexington-class, but none were completed as battlecruisers (two were completed as aircraft carriers). However, during WWII the U.S. commissioned two vessels known as the Alaska and Guam. They were designated "large cruisers", but had some characteristics of battlecruisers. This post will cover the mission for which the Alaskas were designed, their specifications, armament, armor scheme, propulsion, and their operational history.
     At the time the Alaska-class was designed, the Japanese heavy cruisers were becoming a threat to any then-future carrier operations independent from the Battle Force. At the same time, Germany was building the Duetschland-class "pocket battleships" for commerce raiding. France was also rumored to be developing a class of 17,500 ton commerce raiders carrying 12in guns. Thus, a class of ships was needed to be able to escort carriers, and defend the carriers without detracting from the firepower of the Battle Force. At, the same time this class would have to be able to hunt down and kill enemy commerce raiders. This is the niche that was to be filled by the Alaska-class.
      Final design specifications of the Alaska-class are drawn from William Garzke's Battleships: United States Battleships, 1935-1992:

Armor
light ship	25,971 tons
standard	27,000 tons
full load	34,253 tons
Dimensions
length overall	808’ 6” (246.431m)
waterline length	791” 6” (241.249m)
maximum beam	90’ 9.375” (27.670m)
maximum draft	31’ 9.25” (9.684m)
Armament
main battery	9 - 12”/50 (305mm)
secondary	12 - 5”/38 (127mm)
antiaircraft	56 - 40mm/56
	34 - 20mm/76
Armor
main side belt	9.0” tapered to 5.0”, inclined 10 degrees (229mm-127mm)
main deck	1.40” (34mm)
second deck centerline	2.80” + 1.0” (71mm + 25mm)
third deck	0.625” (16mm)
Machinery
shaft horsepower	150,000
maximum speed	33 knots
endurance @ 15 knots	12,000nm

     Armament. The Alaska-class was the last class of ship in the U.S. Navy to carry 12in guns, and probably the last in the world. However, the guns that the Alaskas were equipped with actually outclassed the 14"/45 Marks 1, 2, 3 and 5 guns carried by the New York-class and Pennsylvania-class battleships early in their careers. Specifically the guns carried by the Alaskas had better penetration capabilities than the earlier 14in guns at all ranges*. This was achieved by the use of the Mark 18 "super-heavy" AP shell which weighed in at 1,140lbs (517kg). The main battery turret armor was 325mm on the face, 152-133mm on the sides, and 127mm on the roof. The secondary armament consisted of 12 5"/38 guns in 6 twin mounts. Antiaircraft armament consisted of 56 40mm/56 cannons in 14 quad mounts, and 34 20mm/76 cannons in single mounts.  The massive secondary and anti-aircraft armament carried on the Alaska-class made them immensely valuable for kamikaze defense late in WWII. Had the Alaskas been kept in service after WWII, it is likely their 20mm cannons would have been removed entirely, and their 40mm mounts replaced by the then-new 3"/50 Mark 27 guns.

The Guam in Pearl Harbor in February 1945

     Armor. Armor was as listed above in the specifications. Additional armor numbers are, 280 to 330mm for the barbettes, and 270 mm on the control tower. As to underwater protection, it was almost nonexistent on the Alaska-class. Rather, the Alaskas relied on internal subdivision as protection against torpedo and underwater shell damage.  

      Propulsion. The Alaska-class ships were driven by four sets of General Electric geared turbines. The turbines were driven by eight Babcock & Wilcox Express boilers. The max steam pressure for the boilers was 45kg per square cm. The turbines drove four propellers. Top speed as designed was 33 knots, but the trials showed a top speed of 32.72 knots. Electricity was provided by four generators. Each engine room (there were two) had a single General Electric turbo-generator rested at 1,000kW, 450V AC. At either end of the propulsion spaces were single GE generators each rated at 1,062kW, 450V AC.
      The Alaska-class did suffer from a number of problems. The Alaska-class lacked sufficient space for a CIC, making conditions extremely crowded. The Alaska-class also had relatively thin armor for her displacement, at a time when it was possible to give ships a high speed even with thick armor (see the Iowa-class). The top speed of 32.72 knots achieved during trials lower than what was predicted or designed. Finally, underwater protection aboard the Alaskas was nonexistent. Any conventional side protection scheme was sacrificed to reach higher speeds, and would have left the Alaskas vulnerable to torpedo attack had the Alaska entered the war earlier than they did. This with a displacement approaching that of battleships.
      History. Construction of the Alaska-class was authorized by the Two-Ocean Navy Act in 1940. Six vessels were authorized, of which two were completed, three were cancelled, and one was scrapped before being commissioned. The two vessels that were completed were the Alaska and Guam. The Alaska was laid down on 17 December 1941, and commissioned 17 June 1944. The Guam was laid down on 2 February 1942, and commissioned on 17 September 1944. The third vessel which was constructed, was the Hawaii. She was launched, but never completed (more on the Hawaii later).
        Operational History. The Alaskas both had very short careers. The Alaska first screened aircraft carriers attacking the Japanese Home Islands in March 1945, and destroyed two Japanese aircraft on 18 March. She then participated in shore bombardment of Minami Daito Jima on 27 March, and in late July took part in sweeps of the East China Sea. After the Japanese surrender the Alaska supported minesweeping operations along the Chinese coats, supported Army landings at Inchon on 8 September,  and sailed to Tsingtao to hold the port by force until Marines arrived to take over.  The Guam arrived at Pearl Harbor on 8 February 1945, and sailed for Ulithi on 13 March joining the Alaska. From there the Guam escorted TF 58 on a raid of the Japanese Home Islands, breaking off on 19 March to escort the USS Franklin back to Ulithi. On 27 March the Guam participated in a bombardment of Okinawa. From the Invasion of Okinawa to the end of the war, the Guam participated in a series of raids in the east China Sea and the Chinese coast. After the end of the war the Guam showed the flag along the Chinese coast, and participated in the occupation of Korea.

The Hawaii just prior to the suspension of her construction.

      The Hawaii. The Hawaii was never completed, and she was scrapped in 1959. However, before her scrapping there were two proposals to convert her. One proposal was a conversion to a command ship similar to the Northampton, but larger. This proposal was nixed when it was shown that an escort carrier, the Wright, could the same thing for cheaper. The second proposal was a conversion to a guided missile cruiser, carrying an ASROC launcher, twin Talos SAM launchers, and twin Tartar SAM launchers. Other variants of the missile proposal included fitting the Hawaii with 12 U.S.-built V-2 missiles, or later 20 Polaris ICBMs. In the end the missile proposal was scrapped as being too costly.
      The Alaska-class cruisers were neither battlecruisers or battleships, regardless of their appearance. They were designed from the beginning as a counter to perceived threats from hostile cruisers. Their main armament was meant not for slugging it out with enemy battlewagons (though it is possible the 12/50 Mark 7 may have been better than the 14" guns carried by the Kongo-class battlecruisers), it was meant to overwhelm an enemy heavy cruiser. The mission the Alaskas were designed was by 1944, non-existent, and in hindsight they were unnecessary. They were anachronisms born from the lifting of the Washington Treaty restrictions on cruisers. Regardless of that fact, they served well and were not inherently bad ships.
   


*Unfortunately, I cannot link directly to penetration tables for the 12in/50 and 14in/45 guns. If you wish to compare the penetrations for the guns, the requisite tables are on the NavWeaps pages for each gun.  The NavWeaps pages are linked to in the post.