Jump-Starting Japanese Naval Aviation

By the beginning of World War II in the Pacific, the Imperial Japanese Navy had ten aircraft carriers, advanced naval planes, and some of the most highly trained aviators in the world. Opposing pilots feared the A6M2 Zero fighter, and few Allied ships that were attacked from the sky survived without strong antiaircraft defenses and fighter cover. However, the Japanese naval air arm was not wholly homegrown. It had received help from Great Britain. 

Much of the assistance came courtesy of the Sempill Mission—officially known as the British Aviation Mission to Japan—formed and led by William Forbes-Sempill, a Scotsman who later inherited the title of lord from his father. An aviation pioneer during the Great War, he and other veteran fliers, such as Frederick Rutland and Edwin H. Dunning, were instrumental in the evolution of aircraft carrier operations. 

Born in September 1893, Sempill dropped out of Eton at 16 and set off to invent himself. He developed a reputation and a following early by setting several flying records. In 1914, during the opening days of World War I, he volunteered for the Royal Flying Corps; he later transferred to the Royal Naval Air Service. The two services would later merge to become the Royal Air Force (RAF). At war’s end, Sempill was a colonel in the RAF. By then, the Royal Navy possessed the first flush-deck aircraft carriers and had laid down the first purpose-built carrier. The U.S. and Japanese navies soon followed suit in an effort to stay apace with what some thought might be an important innovation in the future of naval warfare. 

Anglo-Japanese Ties

At the time, British assistance to the Japanese Navy seemed almost natural. Since the service’s inception in 1869 during the Meiji Restoration, it had been modeled on the Royal Navy, and its first steam-powered ships were built in British shipyards. 

In 1902, Japan and Great Britain allied themselves when they signed the Anglo-Japanese Alliance, which bound the two countries to safeguard each other’s interests in Asia. Originally suggested by Great Britain to protect itself against Russian expansion in the region, the treaty proved to be more advantageous to Japan after that country came to blows with Czarist Russia, which was seeking to expand its influence into Manchuria and Korea. The 1904–5 Russo-Japanese War resulted in the first major defeat of a European power by an Asian nation. 

During World War I, while Britain was tied down fighting Germany, the alliance obligated Japan to guard British interests in China. Taking advantage of the pact during the opening months of the Great War, Japan—initially not directly involved in the fighting in Europe—declared war on Germany. In 1914, it seized German possessions in Asia and the western Pacific, namely, the Chinese port of Tsingtao and German Micronesia (the Mariana, Caroline, and Marshall islands). Germany had purchased the island groups from Spain just 15 years earlier. 

Mission to Japan

In the summer of 1920, the Japanese ambassador in London, Hayashi Gonsuke—an erstwhile friend, ally, and admirer of the Royal Navy—asked that an official British naval aviation mission be sent to Japan. The Admiralty was against the proposal, not wanting to help a foreign nation challenge its supremacy, even if it were an ally and guarantor of British interests in Asia. However, other governmental entities, such as the Foreign Office, Air Ministry, and Department of Trade, with a nudge from the British aviation industry, were in favor. As a result, a compromise was reached. The effort would proceed as an unofficial civil aviation mission, but Britain still would come to regret the results a generation later.

Sempill started assembling the mission in early 1921. In September, the delegation’s 30 instructors and support staff arrived at Kasumigaura, outside Tokyo, where the Japanese had begun constructing an air base. Training soon commenced. The mission would include almost 100 British-built aircraft, including Avro 504 K/L trainers, Gloster Sparrowhawk carrier fighter planes, Parnall Panther carrier reconnaissance aircraft, Blackburn Swift and Sopwith Cuckoo Mk II carrier torpedo bombers, Supermarine Seal and Vickers Viking amphibian flying boats, and Felixstowe F.5 flying boats.

Over the following 18 months, the first generation of Japanese aviators was taught how to fly, take off from and land on a carrier deck, and dogfight, and received instruction in navigation and the use of aerial torpedoes. In addition, Sempill Mission experts helped with the design and construction of Japan’s first aircraft carrier, the Hōshō, which had been laid down in 1919. To further this end, the mission arrived with details of the Royal Navy carriers Argus and Hermes. (Ironically, the Hermes would be sunk by Japanese carrier aircraft in the Indian Ocean during the early months of the Pacific war.) Other British advisers not directly involved in flying taught aircraft maintenance, fleet cooperation, armaments, and the use of parachutes and aerial photography. 

Members of the mission received 150 percent of their RAF salaries, plus expenses. They also were given temporary rank in the Imperial Japanese Navy and uniforms designed by Sempill. Capping off the mission was the establishment of shore facilities for floatplanes, maintenance, and instruction. In 1920, the Japanese had begun production of flying boats with the assistance of the British firm Short Brothers. At the conclusion of the mission, the Japanese presented Sempill with the Order of the Rising Sun (Third Class), and other members of the delegation received medals and samurai swords.

Other Advisers to Japan

British aviation companies had hoped the Sempill Mission would result in new orders, but this did not come to pass on a large scale. Instead, Japanese companies copied foreign designs and incorporated them in the manufacture of their own aircraft, Mitsubishi being the primary beneficiary. 

The Sempill Mission was not the full extent of British aid to Japan’s naval aviation efforts. Mitsubishi hired several former British naval aviators as technical advisers and test pilots. These included Frederick J. Rutland, who, while piloting a floatplane, had spotted German warships just prior to the Battle of Jutland; William L. Jordan, the first person to take off from and land on a Japanese carrier—the Hoˉshˉo; and Herbert Smith, a design engineer from the Sopwith Aviation Company. 

In 1930–31—well after the Anglo-Japanese Alliance had lapsed—the Imperial Japanese Navy invited two more British aviators to Japan. At the Yokosuka Naval Base, Lieutenant Commander Roy W. Chappel and a Lieutenant Wingate gave instruction on the latest advances in aerial tactics. One of their students was Lieutenant Minoru Genda, who helped plan the 7 December 1941 attack on Pearl Harbor. 

All these British interwar endeavors gave Japan a giant leap forward in its development of naval aviation. 

British Clandestine Assistance

Sempill evidently had become enamored of Japan—too enamored. After he returned to England in 1923, he remained in contact with the Japanese through their embassy in London, and over the years he passed confidential, and in some cases secret, information related to naval aviation. By 1926, the British Directorate of Military Intelligence had become aware of his activities, but Sempill’s situation was complicated on several levels. It was feared that his prosecution might reveal to the Japanese that their diplomatic codes had been compromised. Also, Sempill took a seat in the House of Lords after the death of his father in 1934 and was a member of Winston Churchill’s inner circle. 

Complicating the situation even further was the fact that Sempill had become associated with Oswald Mosley’s British Union of Fascists and other pro-Nazi and anti-Semitic groups. At the very least, the argument could be made that he was a Japanophile. If he was a spy, he did not go out of his way to hide the fact that he was in the pay of the Japanese. Much of what he shared with his Japanese paymaster had passed through the regular mail.

Among other things, Sempill was not given to living within his means. He almost constantly was in debt, which may have added impetus to his continued efforts to provide the Japanese with whatever they wanted. Despite his nefarious activities, Sempill was given a position in the Admiralty’s Department of Materiel when World War II broke out in 1939.

In May 1940, Mosley was interned for the duration of World War II because of his pro-Nazi activities. Sempill, however, continued to work at the Admiralty. This may have had to do with the fact that Mosley was more outspoken publicly than Sempill and connected with Germany, not Japan, with whom Britain was not yet at war.

However, Frederick Rutland would be interned for spying for Japan. Rutland had retired from the RAF in 1923 after having begun to assist the Japanese Navy covertly. He later joined Mitsubishi as a civilian contractor. He continued to surreptitiously assist the Japanese through the 1920s, 1930s and into the 1940s, having moved to Hawaii in 1933. His espionage activities would end when Japan bombed Pearl Harbor. Back in Britain, he was arrested and interned at the request of the United States. When he finally was released in 1945, he thought he could salvage his reputation. Having failed at that, he took his own life in 1949.

Investigating Wartime Spies

In October 1941, just more than a month before the Japanese attacked Pearl Harbor and British holdings in the Far East, Anthony Blunt of MI5—an arm of the Directorate of Military Intelligence—wrote a report on Japanese intelligence networks throughout the British Empire. At the time, Blunt, as a member of what became known as the Cambridge Five, was spying for the Soviet Union. As he pointed out in his report, Japan ran its networks primarily through its embassies and consulates, which served as collecting points. Besides Japanese nationals gathering intelligence, British citizens, many with pro-Nazi and pro-Japanese sentiments, played a role. 

One British citizen born in New Zealand—Indian Army Captain Patrick Heenan—was caught passing intelligence on the defenses of Singapore to the Japanese embassy in Thailand by way of frequent visits there. He was executed shortly before Japan captured the island colony. Other sources of Japanese intelligence were members of Parliament, the Foreign Office, and the military. Blunt wrote in his report:

On 30 September 1940, Lord Sempill undertook to the Admiralty not to discuss any official matters with the Japanese. Since then, however, he has maintained contact with them, and there are grounds [telephone taps] for supposing he has not broken off his contacts. . . . We cannot conclude from the foregoing that Lord Sempill is consciously acting as an agent for the Japanese, but the risk is a serious one, given that he holds the position he now does in the Admiralty. 

In December, after more evidence of his espionage was discovered, Sempill agreed to retire. To quote Churchill: “At any moment we may be at war with Japan, and here are all these Englishmen, many of them respectable, two of whom I know personally, moving around collecting information and sending it to the Japanese Embassy.”

Road to Pearl Harbor

Through the Sempill Mission and subsequent assistance, British aviation specialists provided the Japanese with expertise, equipment, and training that allowed them to fast-track their naval aviation program almost in lockstep with the Royal Navy. Some have argued that without their help, Pearl Harbor would never have taken place. Or, at the very least, the Japanese Navy would have taken longer to reach the point at which it was able to execute such an audacious carrier strike. 

The Sempill mission undoubtedly was a success in that it provided the training and equipment needed to transform Japanese naval aviation along the lines of what the Royal Navy had accomplished. From the mission’s conclusion in 1923 into the 1930s, Japanese naval aviation expanded rapidly. It is difficult to know how many Japanese aviators went through the program, but by 1930, Japan had three aircraft carriers and more than 100 carrier-based aircraft, matching the respective Royal Navy numbers at that time.