Japanese aircraft carrier Unryū

The Japanese aircraft carrier  Unryū (雲龍) was a fleet aircraft carrier of the Imperial Japanese Navy which served during World War II. She was commissioned on 6 August 1944 and eventually torpedoed and sunk by US submarine USS Redfish (SS-395) in the East China Sea on 19 December that same year. The name Unryū means literally "cloud dragon."

Design
Unryū was one of six fleet carriers laid down by the Imperial Japanese Navy in 1942-43 as part of the Navy's War Construction Program. In order to expedite building of the new carriers, a standard design was chosen based on ease of manufacture and availability of materials. The Hiryū, with her high speed, good seakeeping and relatively large air group, required far less armor plate and use of special machinery than needed for the Shōkaku class and Taihō class carriers, making her the ideal candidate and the design was quickly adopted with only a few modifications.

Other ships of the Unryū class included Katsuragi, Amagi, Kasagi, Ikoma and Aso. A further eleven examples were ordered in 1942 but work on all ships of the class was suspended in 1945 when worsening wartime conditions left even those carriers already completed (Unryū, Katsuragi and Amagi) virtually inoperational due to a lack of aircraft, aircrews and fuel oil.

Hull
Unryū's hull form was virtually identical to that of Hiryū with the exception that, since the carrier's island was now located on the starboard side of the flight deck, the width of the hull on her port side was increased in order to balance the transfer of weight. As in Hiryū, the hull was not bulged and the only anti-torpedo defense was the 150 mm waterline belt armor abreast the machinery and magazines, tapering down to 90 mm where the aviation fuel tanks were located at either end of the ship. The partial 20 mm internal anti-splinter bulkhead was also retained. Deck armor was again limited to 25 mm over the machinery spaces and 55 mm over the fore and aft ordnance magazines and AvGas tanks, giving the carrier scant protection from plunging shellfire or armor-piercing bombs.

The carrier's aviation fuel tanks were still made integral with the ship's hull, a standard practice in Japanese carrier design that heightened the risks of fuel fires due to cracks and leaks developing from sudden shocks to the hull, whether from torpedo hits or bomb near-misses. In a concession to later wartime experience, aviation fuel capacity in the Unryū-class carriers was cut from 150,000 gallons to 48,000 gallons as it had been found that most Japanese carriers damaged or sunk during combat had time to use only a small proportion of their available AvGas. The empty air spaces around the aviation fuel tanks were also filled in with concrete as added splinter protection.

Machinery
The same cruiser-type machinery as had been used in Sōryū and Hiryū was installed on Unryū. The four sets of geared turbines had an output of 152000 shp and were connected to four separate shafts, giving Unryu a top speed of 34 kn during sea trials. Steam was generated from eight oil-fired Kampon boilers. Unryū's standard fuel oil capacity of 3670 tons gave her a radius of 8000 nmi at 18 kn.

Flight Deck & Hangars
Unryū's wooden-planked flight deck was 217 m long by 27 m wide and retained the standard arrangement of nine hydraulically controlled Type 3 arrester wires as used on Hiryū, three forward and six aft. These were capable of stopping a 6000 kg aircraft at speeds of 60-78 knots. The three forward wires allowed Unryū to recover aircraft over the bows while steaming astern in the event the after end of the flight deck was rendered unusable due to bomb damage or during periods of excessively high winds.

The upper hangar measured 175 m long by 21 m wide while the lower hangar, though of the same width, was appreciably shorter at 130 m. They featured the standard fireproofed fabric dividing curtains and twin rows of foam-dispensing pipes and nozzles running along the hangar walls and ends as had been installed on earlier Japanese carriers. The curtains served to limit the supply of air to and delay the spread of any fires breaking out on either deck while the foam suppression system worked to extinguish the blaze.

In order to save on building time and materials, only two aircraft elevators were installed fore and aft, the aft elevator being an entirely new design, roughly pentagonal in shape, measuring 14.2 m by 14.2 m. Both elevators had the same load limit of 5000 kg as those on the Sōryū-class carriers. The absence of an amidships elevator increased available floor space on the upper and lower hangar decks by 276 m2 but total aircraft capacity remained unchanged due to the fact that Unryū was expected to operate the larger carrier-plane types just coming into service at the time of her completion.

The carrier's starboard-side island was larger than that of Hiryū's but was offset enough that it did not encroach on the width of the flight deck.

Two Type 21 air-warning and control radars with mattress-type antennas were installed, one atop the island and the other on a retractable pillbox on the port side aft edge of the flight deck. Two Type 13 radars were also added, one on the main-mast abaft the island and the other attached to one of the two hinged radio masts on the ship's aft starboard side. The Type 21 radar had a maximum effective range of 80 nmi while the Type 13 had a range of 54 nmi

Armor, armament and sensors
Unryū's waterline armored belt was 1.8 in thick over her machinery spaced, but this increased to 5.5 in over her magazines. Her deck armor above the magazines was 25 mm thick, but the deck above the magazines was 2.2 in thick.

The ship's primary armament consisted of a dozen 40-caliber 12.7 cm Type 89 anti-aircraft (AA) guns in twin mounts on sponsons on the ship's sides. Unryū was initially equipped with 16 triple 25 mm Type 96 and three single AA gun mounts, most on sponsons along the sides of the hull. By the end of the war, the ship mounted 22 triple and 23 single mounts. These guns were supplemented by six 28-round AA rocket launchers. For defense against submarines, the carrier was fitted with six depth charge throwers and carried between six and ten depth charges for them.

Two Type 94 high-angle fire-control directors, one on each side of the ship, were fitted to control the Type 89 guns. Each director mounted a 4.5 m rangefinder. Six Type 95 directors controlled the 25 mm guns and the 12 cm rocket launchers. Early warning was provided by two Type 2, Mark 2, Model 1 air search radars. One of these was mounted on the top of the island while the other retracted into the port side of the flight deck, between the two elevators. In addition, Unryū had two smaller Type 3, Mark 1, Model 3 air search radars, one mounted on the tripod mast on the island and the other on the aft starboard retractable radio mast.

Final voyage
On 13 December 1944, thirty "Ōhka" suicide rockets of the Thunder-Gods Corps were loaded aboard Unryū for transport to the port city of Manila in the Philippines. Four days later, on 17 December 1944, Unryū departed Kure, Hiroshima escorted by Shigure, Hinoki, and Momi under the overall command of Captain Konishi. Her maiden sea voyage was a vain attempt to reinforce the garrison on the island of Luzon just prior to the US landings there.

On 19 December 1944, Unryū was torpedoed and sunk by the submarine USS Redfish. Redfish fired four bow torpedoes, one of which hit directly under the carrier's bridge on the starboard side at 16:35, stopping the vessel dead in the water. Unryū engaged with all her starboard side guns. A second torpedo struck at 16:50 on the starboard side abreast the forward elevator, just as the carrier was managing to get under way again. The resulting explosion set off the Ohka suicide planes stored on the lower hangar deck as well as the highly volatile aviation fuel underneath.

Once the boiler rooms flooded, the ship listed to 30 degrees and the order to abandon ship was given. With a 90 degree list, the ship sank to the bed of the East China Sea in just seven minutes at position 29.98333°N, 124.05°W. Casualties were great: Captain Kaname Konishi and 1,238 officers and men lost their lives. Only one officer and 146 men survived and were rescued by the escort destroyer Shigure, which returned to Sasebo, Nagasaki on 22 December.