Evolution of the Aircraft Carrier: Part 13: IJN Ryujo by Dan Linton
Writer: Dan Linton


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IJN Ryujo and the Shadow Program


Part 13: IJN Ryujo and the ‘Shadow Program’

The London Naval Conferences of 1930 and 1934:

The London Naval Conference of 1930 led to a Treaty which fundamentally extended the provisions of the Washington Naval Treaty another five years into the future. Japanese nationalists and many military officers disparaged this signing as “the May 15th Affair” (1) and as the 1930’s began, pressures on the liberal administrations in Japan from the Depression, the Americans raising their tariffs (2), and the Army seeming to be out of control and creating incidents that lead to the seizure of Manchuria (1931-1933) – all these the administrations could not handle. A number of political assassinations occurred and most often the perpetrator was a junior officer. By the end of 1933 the militarists were in the ascendant and Japan took itself out of the League of Nations. At the preliminary conference in 1934 in London, set to prepare for another five-year renewal of the London Treaty, the Japanese delegates demanded an end to the 5:5:3 ratios of British, American, and Japanese fleets, claiming only full equality was acceptable. The British and American delegates refused, and on December 29, 1934, Japan gave formal notice that after December 31, 1936, she would no longer be bound by the terms of the Washington and London Naval Treaties. A new naval race was on (3), to be detailed in the next and last article in this series.

IJN Ryujo: the Shoe that wouldn't Fit


IJN Akagi and IJN Kaga took up 58,000 (officially) of the 81,000 tons for carriers allowed by Treaty for the Japanese navy. But Japan did not design and build the 23,000 ton carrier the Treaty allowed. Mindful of the idea, current in the USN, that the number of decks was more important than size of the ship (thus the design in 1929 of USS Ranger, CV-4), the Japanese in 1929 tried to squeeze a useful load of aircraft onto a small hull. A clause in the Treaty defined an aircraft carrier as a ship of “at least 10,000 tons”: if the Japanese could build a useful ship of less displacement, it would not count against Treaty tonnage and might be repeated to provide numerous flight decks. The result of this thinking was IJN Ryujo (4) officially designated as displacing 8,000 tons standard. It was laid down in 1929 as a flush-deck carrier with a starboard trunked exhaust. (picture 1 above, and 2, 3 below) It had no armour nor heavy 8” guns, and its single hangar could accommodate 24 aircraft. While building, the design was modified to accommodate a second hangar, raising its aircraft capacity to 48. Now displacing 12,500 tons standard, she was still ‘officially’ listed as below 10,000 tons standard displacement. She was launched in 1933 but her stability was suspect and she was taken almost immediately back into the yards for new hull bulges, adding of ballast to the keel, and lightening areas above the waterline as much as possible (e.g. removal of some anti-aircraft guns). After barely surviving a severe storm in 1935, her forecastle was raised but she was never ‘trusted’ and, as had happened with Ranger, was considered a second-line unit. (5) Her small aft elevator (35’ x 26’) was almost useless; by the time of the war, aircraft having grown in size and weight, she was in reality a single-lift carrier with a short take-off deck and only small strike packages could be arranged at any given time. (6) Overall, Ryujo was 590’ x 68’ x 23’ draught (181m x 20.9 m x 7m) but her flight deck was only 513’ x 75’ (157.8m x 23m). (pictures 4,5, and 6) She could manage 29 knots but without armour or longitudinal strength she was relegated to secondary duties. (pictures 7-12) She covered the landings in the Philippines in December, 1941; the invasion of Java in February, 1942; took part in the Indian Ocean operation in April, 1942; and was part of the Aleutian diversion force in June, 1942 when the main Japanese strike force went to Midway. She was lost in August, 1942, being successfully attacked by aircraft from USS Saratoga CV-3. (7) Perhaps the most striking aspect of this strange ship was the location of the navigating bridge, just under the flight deck as seen in the main picture of this article.


Click on the images to enlarge!

The Hybrid Temptation:

The Hybrid Temptation:

The previous article in this series outlined briefly how the USN authorized, and almost built, a cruiser-carrier to take advantage of the clause in the 1930 London Treaty allowing flight decks on one-quarter of available cruiser tonnage. The Japanese designed a hybrid carrier-cruiser. Picture 13 (above) shows the G6 design of 1932. In size (displacement and dimensions) the G6 could only have been called a carrier and yet since it could be argued that carrying aircraft was not its primary purpose, it might slip by. The G8 design seen at the bottom of the diagrams, the original design for the Soryu class, is more “carrier-like” than the G6 design, yet it still has cruiser size guns and turrets. This particular design also has a closed quarterdeck, much in the manner of British carriers from Ark Royal (1937) to the WWII fleet carriers. Once it was realized that Japan would not ratify any extension of the London Treaty, and would in fact give notice of its abrogation, then there was no longer pressure to compromise, and like the Americans, the Japanese dropped the idea of the cruiser-carrier. (8) In the 1930’s the Japanese had developed cruisers that were a match to any being built anywhere on earth and many admirals did not want to ‘lose’ cruisers for the sake of a few aircraft.

The Shadow Fleet:

The Japanese, limited by Treaty to only 3/5ths the tonnage of the USN, nevertheless wanted as many flight decks for the IJN as the Americans had. It would have been very interesting had the Soryu-hybrids been built to see the American reaction. As it was, the Soryu as built and the later Hiryu were outside of any Treaty restrictions, but how could Japan with half the population and much less industrial capacity than the United States possibly keep up? One way was to spend prodigiously: by the end of the 1930’s the IJN was taking up 30% of the entire Imperial budget, a fact not lost on Army officers who by then were involved in a full-scale war in China. The other way was through the ‘Shadow Fleet’. The ‘Shadow Fleet’ was the name given to a program of construction of auxiliaries and even passenger liners that were built with the intention that they could be quickly converted into aircraft carriers. Since flight decks on Japanese carriers were simply steel frameworks built above the main deck, which then became the hangar deck (as in USN carriers), it was felt that these conversions could be done quickly, and in many cases they were.

Two high-speed oilers were to have been laid down in 1934 but they were in fact built as submarine tenders. IJN Tsurugisaki (picture 14, above) spent only two years as a tender before being taken in hand and completed as the carrier Shoho, or Happy Phoenix (pictures 15 and 16). Unhappily, however, Shoho became the first IJN carrier destroyed, being sunk during the Battle of the Coral Sea in May 1942. Her sister ship was the Takasaki but even before she was completed as a submarine tender, she was taken in hand and converted into the carrier Zuiho (Lucky Phoenix). Her conversion was completed in January, 1942. (9)(picture 17 and picture 18, showing late war flight deck ‘camouflage’, seen as the lead picture of this paragraph above) The liners Kashiwara Maru and Izumo Maru both laid down in 1939, their construction partly subsidized by the IJN, but were taken in hand and were converted into the Hiyo, or ‘Happy Falcon’ (picture 19) and Junyo, or ‘Wandering Falcon’ (pictures 20 and 21). Ryuho or ‘Dragon Phoenix’ was a submarine tender built in 1934 as Taigei (picture 22) but converted from December 1941 to November 1942. It was a second-line unit (picture 23) and one of only three Japanese carriers (out of 25 and two battleship-carrier hybrids) to survive the war. Chitose (picture 24) was a high-speed seaplane tender completed just before the war began but converted to a carrier (picture 25) from January 1943 to January 1944. Its sister ship, Chiyoda (picture 26) underwent conversion at the same time. (10) This program for creating extra flight decks for the fleet was not very successful: except for Hiyo and Junyo the air wings were small, usually 30 or less, and these ships often did not have the speed, and certainly none of the armour, of the purpose-built fleet carriers. The problem with a ‘shadow’ is that if it is too large, then it is obvious what the intention is – a 30,000 ton submarine tender would have been a very suspect project indeed, and a waste of time and money. Nevertheless, when WWII began, Japan had as many flight decks as the USN.


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More Shadow Fleet:

More Shadow Fleet:

At the time the ‘Shadow Fleet’ program had begun, the concept of an ‘escort carrier’ was rather hazy in the minds of naval strategists. It would be the British in 1940 who would convert merchantmen into ‘escort carriers’ and use them for convoy protection in the North Atlantic. Soon, purpose-built escort carriers would be produced by the score in the United States. In Japan, what became an ‘escort carrier’ was simply a ship too slow or too small of an air wing to work effectively with the main fleet. Three passenger liners were subsidized by the IJN in 1937: their design was meant to be converted to a carrier within six months of being taken in hand. These Nitta Maru class liners were 17,800 ton ships and such a size would be closer to that of a fleet carrier but they could only do 21 knots and carry 21-30 aircraft. Kasuga Maru became Taiyo or ‘Great Hawk’, conversion complete by September, 1941. (picture 27, above) Nitta Maru (picture 28) became Chuyo or ‘Heaven-Bound Hawk’ by November, 1941(picture 29) and Yawata Maru (picture 30) became Unyo or ‘Cloud Hawk’ by May of 1942. (picture 31) The Argentina Maru, completed in 1938, (picture 32) was converted by November, 1943 into Kaiyo or ‘Sea Hawk’ (picture 33) and used as a training carrier and aircraft ferry. The last conversion was the German liner Scharnhorst,(picture 34) stuck in Kobe when war broke out in Europe. In 1940 she was taken over by the Japanese government and converted into a troopship. After Midway, however, flight decks were needed and by September, 1942 she was taken in hand to become the Shinyo or ‘God Hawk’ (picture 35). As with so many other IJN vessels, all these escort carriers fell victim to submarines or carrier air attacks. (11)

Click on the images to enlarge!

Modeling IJN Ryujo

Ryujo, and virtually every one of the twenty-five carriers and two battleship-carrier hybrid conversions has been modeled in plastic in 1:700 scale. Decades ago four companies in Japan, Aoshima, Fujimi, Hasegawa, and I think Pit-Road basically divided up the entire Pacific War fleets, Japanese and American, and a few British ships, amongst themselves to cover every combatant. It is unlikely, given the expense involved, and competition from Chinese manufacturers, that a similar gentleman’s agreement could be arranged for the increasingly popular 1:350 scale. In the case of Ryujo, it was Fujimi that produced the 1:700 kit which can be made into a beautiful model – see picture 36 that heads this paragraph. Pictures 37 and 38 show box art from more than ten years ago and the latest iteration – in the past the Ryujo kit has come with a wood flight deck, a photo-etch fret, and both. But except for the metal 1:1250 offerings, and the 1:700 kit, there is nothing. Nor are there any decent plans to be found for what is undoubtedly a unique, strange-looking, ship.

Next and Last: Part 14: The Last Five Years Before the War.

Click on the images to enlarge!

Endnotes and Bibliography:

1.Macdonald, S., “Evolution of the Aircraft Carrier: Japanese Developments” , p.41

2. The prime earner of foreign currency for the Japanese economy was textiles – cheap cottons and expensive silks – and her major customer was the United States. In 1930 the Hawley-Smoot Act raised American tariffs to 50% on all imported goods, the highest in American history. This blow to the Japanese economy led many (business and military alike) to conclude that foreign ‘adventures’ would be the best way to restore honour and gain new markets.

3. Strangely, the talks did not collapse. In an effort to ‘control’ or at least limit German re-armament, the policy of appeasement led to the Germans being included in the London Naval Treaty, having a ratio similar to that of France and Italy of 1.75 of the size of the British fleet. And it allowed Germany to build submarines.

4. Japanese carrier names are often poetic but are difficult to translate into other languages. Macdonald, op. cit., gives ‘Galloping Dragon’ for ‘Ryujo’ while Stille, Imperial Japanese Navy Aircraft Carriers 1921-1945 gives “Heavenly Dragon” and on the www.combinedfleet.com/ijnnames.htm will be found ‘such as a dragon builds’ or ‘Sacred Dragon’

5. Pettie, M., Sunburst: the Rise of Japanese Naval Air Power 1909-1941, pp.59-60; Macdonald, op. cit., p.41

6. Pettie, op. cit., p.237

7.Stille, op. cit., pp.14-15

8. Evans and Pettie, Kaigun: Strategy, Tactics, and Technology in the Imperial Japanese Navy 1887-1941, p.318 The idea of the hybrid would be resurrected during WWII and lead to the creation of battleship-carrier hybrids, the most famous of which was IJN Ise

9. Stille, op. cit., p.22

10. Ibid., pp.22-24 and 33-34. Chitose and Chiyoda, named after cities, were not re-named after conversion.

11. Ibid., pp. 40-43


Evans, and Pettie, Mark R., Kaigun: Strategy, Tactics, and Technology in the Imperial Japanese Navy 1887-1941, Naval Institute Press, 1997

Jentschurra, Jung and Mikel, Warships of the Imperial Japanese Navy 1869-1945, Arms and Armour Press, 1977 (originally Die Japanischen Kreigschiffe)

Macdonald, Scott, “Evolution of the Aircraft Carrier: Japanese Developments”, in Naval Aviation News, October, 1962

Pettie, Mark R., Sunburst: the Rise of Japanese Naval Air Power 1909-1941, Naval Institute Press, 2001

Stille, Mark, Imperial Japanese Navy Aircraft Carriers 1921-1945, Osprey Publishing, 2005


Picture Credits:

Picture Credits:

Main Picture: IJN, public domain

Last Picture: www.imageshack.us

Picture 1: IJN, public domain

Picture 2: IJN, public domain (haze grey website)

Picture 3: IJN, public domain

Picture 4: www.imageshack.us

Picture 5: IJN, public domain

Picture 6: IJN, public domain

Picture 7: NavSource NH 42271

Picture 8: www.imageshack.us

Picture 9: haze grey website

Picture 10: IJN, public domain

Picture 11: haze grey website

Picture 12: combined fleet website

Picture 13: Jentschurra, p.46

Picture 14: Maritime History and Science Museum, Kure

Picture 15: Maritime History and Science Museum, Kure

Picture 16: Polish website

Picture 17: retouched IJN photo

Picture 18: USN, public domain

Picture 19: IJN, public domain

Picture 20: NARA

Picture 21: NARA

Picture 22: IJN, public domain

Picture 23: Maritime History and Science Museum, Kure

Picture 24: IJN, public domain

Picture 25: Maritime History and Science Museum, Kure

Picture 26: Maritime History and Science Museum, Kure

Picture 27: Maritime History and Science Museum, Kure

Picture 28: Maritime History and Science Museum, Kure

Picture 29: Maritime History and Science Museum, Kure

Picture 30: IJN, public domain

Picture 31: IJN, public domain

Picture 32: USMC 515537

Picture 33: IJN, public domain

Picture 34: unaccredited picture

Picture 35: IJN, public domain

Picture 36:

Picture 37: HobbyLandJapan website

Picture 38: HobbyLandJapan website


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  Photos and text © 2013 by Dan Linton

November 13, 2013