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Lead-gray clouds gathered over Yokosuka naval base on Sept. 6 as Nobuo Kishi, Japan’s defense minister, took a tour of the HMS Queen Elizabeth aircraft carrier, deployed by the British Navy as part of multinational operations to crank up security in the region amid rising tensions with China.

The purpose of the deployment was to “signal the start of a commitment” to a region whose “prominence … is rising significantly,” Commodore Steve Moorhouse said during a briefing on the deck of the ship as 18 F-35B stealth fighters, whose short takeoffs and vertical landings were discussed during Kishi’s inspection, sat on display in a line behind him.

What the $4.1 billion vessel’s former captain didn’t mention was that the visit marked almost exactly 100 years since another British naval mission landed in Japan — one that was commended for its purported achievements, but ultimately led to intelligence leaks that were at least in part to blame for Japan’s audacious attack on Pearl Harbor in 1941.

The Sempill Mission docked at Yokohama in September 1921, a 29-strong team of naval aviators and engineers that took its name from its leader, Cmdr. William Francis Forbes Sempill, a decorated World War I aviator and son of a Scottish lord.

The team’s remit was to help develop Japan’s fledgling aero-naval forces by training officers in technological and operational aspects of naval aviation. It was also charged with teaching takeoff and landing procedures for the Imperial Japanese Navy’s soon-to-be-completed Hosho — the world’s first commissioned aircraft carrier.

Japan’s limited role in World War I, coupled with the technological advances made by Britain and other Western powers, meant Japan had fallen behind, especially in its air power capabilities, says retired Lt. Col. Jun Yagisawa, a researcher at the National Defense Research Institute’s Center for Military History.

In early 1918, when Britain established the world’s first independent air force whose pilots were apportioned specialist bomber, fighter and trench strafer duties, the only aircraft that the Imperial Navy possessed were reconnaissance floatplanes, says Yagisawa, whose research reveals other disparities, such as the overall military aircraft production of each country between 1915 and 1918: 55,746 in Britain against 15 in Japan.

A British delegation attends the opening of the Imperial Japanese Navy Aeronautical Technology and Training Center at an air base in Kasumigaura, Ibaraki Prefecture, in 1921. | COURTESY OF KAGETSURO RESTAURANT, KASUMIGAURA
A British delegation attends the opening of the Imperial Japanese Navy Aeronautical Technology and Training Center at an air base in Kasumigaura, Ibaraki Prefecture, in 1921. | COURTESY OF KAGETSURO RESTAURANT, KASUMIGAURA

Another factor that would increase the need for naval air force capacity was the signing in 1922 of the Washington Naval Treaty by Japan, Britain, the United States, France and Italy, which limited naval construction.

Japan was also a long way off being able to execute aircraft landings or takeoffs from the Hosho, which itself had some fundamental design faults, Yagisawa adds. By inviting specialists from overseas, Japan was looking to catch up — and fast.

“The British Navy had a reputation for possessing the world’s most advanced technology,” says Yagisawa, whose work includes “The Birth and Development of Air Power in Japan 1900-1945.”

“Japan wanted to tap into that, and while Britain’s air force was willing to cooperate, its navy … didn’t want to hand over technology they had sacrificed so much to develop.”

However, a combination of longstanding ties, starting in 1867 with the civil war-curtailed Tracey Mission to train shogunal cadets, and the signing of the Anglo-Japanese Alliance in 1902, plus the not-insignificant consideration of potential contracts for British aircraft manufacturers, prompted a compromise.

Sempill was chosen to head the quasi-official team, but while his wartime achievements and status were certain to impress, his retirement from military duty was probably a more important consideration, Yagisawa says.

“An ex-serviceman wouldn’t be party to the most recent technological developments,” he says. “In fact, it’s notable that the entire mission was made up of former serviceman.”

This guardedness was reflected in the aircraft that Britain supplied to Japan for training, among them 10 F5s, a “flying boat” much lauded during World War I, but which Sempill admitted in one correspondence was “out of date.”

When the Imperial Navy learned this, Lt. Col. Takamaro Ozeki urged Sempill to secure those of “improved design” even before his arrival at the Kasumigaura military base in Ibaraki Prefecture, where the mission would be stationed.

It would be the first of many occasions when the Scotsman would utilize his resourcefulness and connections to please his employer, of whom he says in one letter: “I am entirely at (your) disposal and … straining every nerve to meet (your) wishes.”

William Sempill (far left) and his wife, Eileen (front row, center), pose for a photo at the Kagetsuro restaurant in Kasumigaura, Ibaraki Prefecture, in 1921. | COURTESY OF KAGETSURO RESTAURANT, KASUMIGAURA
William Sempill (far left) and his wife, Eileen (front row, center), pose for a photo at the Kagetsuro restaurant in Kasumigaura, Ibaraki Prefecture, in 1921. | COURTESY OF KAGETSURO RESTAURANT, KASUMIGAURA

The limited correspondences that survive in the Japan National Archives between what Yagisawa calls the “notoriously tight-lipped” Imperial Navy and “Captain The Master of Sempill,” as he was addressed, are strikingly humdrum. Most consist of invitations to various functions, requests for furniture for the officers’ quarters, or quibbles over pay, unruly, light-fingered Japanese staff and leaking lavatories.

In one, an appeal is made to replace the “entirely unsatisfactory” chef at the officers’ mess with one who is more accustomed to “the English style” in order to avoid “discontent and trouble.” (A Mr. S. Ozeki, chef at the Seyoken — a pioneer in foreign cuisine in Japan since 1872 and still operating today — is drafted in, and his menus include porridge for breakfast, steak and kidney pie for Sunday lunch and braised duck with turnips for Wednesday dinner).

Some letters express more serious grievances (one inquires why advice on the lengthening of the Hosho’s flight deck had been ignored), while others are cringingly self-serving, such as Sempill’s request that remunerations be kept secret to avoid “friction” with Japanese officers: At £5,000 (about ¥37.5 million today), Sempill’s salary was more than double that of his Japanese peers.

However, extant records from the British side — most of them letters, telegrams and memos dated after the completion of the Sempill Mission — could have come straight out of a John le Carre novel.

“Be very careful how you use any information you get,” he writes in a Dec. 10, 1924 letter to Japanese naval attache Cmdr. Teijiro Toyoda that’s double-enveloped and labeled “STRICTLY SECRET.” “And don’t couple the name of any individuals with it. … I know just exactly how the wind blows and the need for being supercautious.”

By this time, Sempill’s correspondences and phone calls were being monitored by MI5, Britain’s counterespionage agency.

According to one memo, concerns were first raised in early 1924, not long after Sempill’s return to Britain, “on account of a suspicion he was trying to obtain certain confidential information about bombs on behalf of the Japanese Navy.”

Other intercepted documents seemed to confirm these fears, containing information on other sensitive technology, including aircraft sound detectors and a cutting-edge seaplane code-named “Iris,” both top secret projects still under development in Britain at the time.

“In 1926, he was interrogated after MI5 judged he had cooperated with the Japanese,” says Ken Kotani, a professor at Nihon University who spent two years in Britain studying the intelligence documents after they were declassified. “Despite having no further obligation toward the Japanese, he maintained contact, sometimes visiting Royal Navy docks, or bases and passed on highly sensitive, technical information. It’s difficult to understand what motivated him, keeping in mind the considerable risk.”

Ken Kotani, a professor at Nihon University, isn’t sure what could have motivated William Sempill to pass on intelligence information to Japan. | ROB GILHOOLY
Ken Kotani, a professor at Nihon University, isn’t sure what could have motivated William Sempill to pass on intelligence information to Japan. | ROB GILHOOLY

While some researchers suggest Sempill developed a deep respect for Japan, others such as Richard Aldrich, a professor of international security at Britain’s Warwick University and a leading historian of the British intelligence services, point to his right-wing sympathies, saying he was “consistently pro-Japan, and pro-Germany” (which was not entirely unusual among the British aristocracy between the world wars).

Britain’s National Archives, where the documents are stored, blame nothing more than his “impetuous character” and “flawed judgment.”

Meanwhile, Antony Best, a history professor at the London School of Economics, believes there was a more fundamental driving force.

Sempill may have been a Scottish aristocrat, but he was an “impecunious noble” who “consistently lived beyond his means,” says Best, an Anglo-Japanese history and intelligence expert who has written widely on Sempill and other British officers suspected of spying for Japan between the two world wars.

“A part of it, presumably, is indulging his passion for flying. That’s what he enjoys — flying and fast cars,” Best says. “He’s a thrill-seeker and one of the reasons why he’s susceptible to engage in activities that he really shouldn’t engage in is he needs the money. He’s exactly the wrong material to have in a highly sensitive position.”

Records confirm this improvidence had left Sempill with debt totaling what today would amount to around £800,000 (¥125 million).

Even after being investigated, he continued to search for overseas “consultancy” work — Russia, Afghanistan, Greece and Chile among them — boasting of his experience in gunnery and working with and flying “practically every type of machine.”

“He passed on British Navy technological information to other countries as well, directly, sometimes openly,” says Kotani, whose published works include “A History of Anglo-Japanese Intelligence Warfare: Churchill and the Pacific War.” “And it’s clear, too, he continued to be hired by the Japanese Navy as a kind of spy.”

The HMS Queen Elizabeth docked at Yokosuka naval base in early September as part of multinational operations to crank up security in the region amid rising tensions with China. | © CROWN 2021 / VIA THE SEMPILL MISSION AND U.K.-JAPAN NAVAL RELATIONS
The HMS Queen Elizabeth docked at Yokosuka naval base in early September as part of multinational operations to crank up security in the region amid rising tensions with China. | © CROWN 2021 / VIA THE SEMPILL MISSION AND U.K.-JAPAN NAVAL RELATIONS

Some information was injudiciously relayed to Sempill via an employee at the Air Ministry, who was eventually rooted out and fired. Blackburns, the manufacturer of the Iris, also faced sanctions. Yet, Sempill got away scot-free, a result, some believe, of his heritage and the fact his father had royal connections.

In fact, when World War II broke out in Europe in 1939, Sempill was invited by Winston Churchill, then navy minister, to spearhead the ministry’s Air Material Division, home to information about the most cutting-edge technology.

At that time, Sempill had pledged not to engage in any military-related exchanges with Japan. But in 1941, when the contents of a secret meeting between Churchill, who by then was prime minister, and U.S. President Franklin D. Roosevelt were deciphered in a telegram sent from the Japanese Embassy in London to Japan, few inside MI5 had any doubt as to the culprit.

But still Sempill wasn’t arrested, which experts say was both an attempt by Churchill to avoid revealing Britain’s codebreaking activities and dodge an unwanted scandal, particularly in light of the disastrous developments at the time.

“(In 1941 and 1942), the war is not going well for Churchill… so the last thing he wants is a major security scandal, where it’s revealed he has effectively handed over secrets to someone who’s close to both Japan and Germany,” says Aldrich, adding that shortly after his meeting with Roosevelt, Britain’s leader had tea with Sempill, who then “popped round” to the Japanese Embassy in London. “So, he’s sent off to an obscure posting in Scotland and basically placed in quarantine, where he can’t do any more damage.”

By then, however, the damage had been done. Aldrich calls Sempill a “big fish” when it came to the meteoric rise of Japan’s naval air power (apart from his other indiscretions, it’s believed he took with him to Japan plans of Britain’s “Argus” — the world’s first full-length flat deck aircraft carrier, and likely the basis of retrofits to the Hosho.)

Indeed, along with several of his British aviator-turned-spy contemporaries, such as Frederick Rutland, who had trained Hosho pilots in Japan immediately after Sempill (and later spied for Japan in the United States and Singapore), he had helped precipitate a carrier fleet to rival Britain’s, without which Pearl Harbor might never have happened.

Even while banished, Sempill continued to work with Japan in the postwar years, becoming connected to a number of causes and organizations trying to “rehabilitate” his former employer, Aldridge says.

He was instrumental in establishing the Anglo-Japanese Association, set up under the auspices of the Japan Society to carry out essentially pro-Japan propaganda.

Understandably, Japan showed its appreciation. Through that same association, it conferred on Sempill the Orders of the Sacred Treasure in 1961 for his “tremendous efforts in Anglo-Japanese rapprochement,” accompanying the Order of the Rising Sun, awarded (but seemingly rejected by Sempill as not fit “for captains”) in late 1922 for what then-Prime Minister Tomosaburo Kato called the “invaluable” and “almost epoch-making” achievements of the mission (albeit in a missive written at Sempill’s behest).

The mission’s success is clouded by reports of mental illness, even deaths, among officers on both sides and a disputed claim in a local newspaper of discontent among instructors regarding the sluggish progress. At the very least, however, it helped ensure the recommencement of Anglo-Japanese relations, exemplified by the recent visit of the HMS Queen Elizabeth, says Nihon University’s Kotani.

“Britain has great influence in the diplomatic and intelligence arenas, where Japan doesn’t,” Kotani says. “But I think Japan can contribute to Britain in other ways — in the economic and technology fields. … Both countries are coming face-to-face with China, so I think they can shake hands for future cooperation.”

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