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The Attack on Pearl Harbor by Alan Zimm

The Attack on Pearl Harbor: Strategy, Combat, Myths and Deceptions (Haverton, PA/Newbury: Casemate, 2011) by Alan D. Zimm analyses the Japanese attack on Pearl Harbor on 7 December 1941 by use of operation research techniques.

Casemate, the publisher, say that the book asks:

Questions never before asked or answered on the Japanese attack from an operational and tactical perspective.
The attack on Pearl Harbor on 7 December, 1941, has been portrayed by historians as a dazzling success, “brilliantly conceived and meticulously planned”. With most historians concentrating on command errors and the story of participants’ experiences, this book presents a detailed evaluation of the Japanese attack on Pearl Harbor on an operational and tactical level.
It examines such questions as: Was the strategy underlying the attack sound? Were there flaws in planning or execution? How did Japanese military culture influence the planning? How risky was the attack? What did the Japanese expect to achieve, balanced against what they did achieve? What might have been the results if the attack had not benefited from the mistakes of the American commanders? The book also addresses the body of folklore about the attack, supporting or challenging many contentious issues such as the skill level of the Japanese aircrew, whether midget submarines torpedoed Oklahoma and Arizona, as has been recently claimed, whether the Japanese ever really considered launching a third wave attack, and what the consequences might have been.
In addition, the analysis has detected for the first time a body of deceptions that a prominent Japanese participant in the attack placed into the historical record, most likely to conceal his blunders and enhance his reputation. The centrepiece of the book is an analysis using modern Operations Research methods and computer simulations, as well as combat models developed between 1922 and 1946 at the U.S. Naval War College. The analysis puts a new light on the strategy and tactics employed by Yamamoto to open the Pacific War, and a dramatically different appraisal of the effectiveness of the attack on Pearl Harbor.

Zimm subjects the strategy behind the attack, the tactical plan and the actual attack to detailed analysis. He uses the assumptions made by the US Naval War College in its wargames and the outcome of other actions in the Pacific War to evaluate the likely outcomes of various options for both sides.

According to Zimm, Admiral Yamamoto Isoruku, commander of the Japanese Combined Fleet, wanted to sink at least one battleship as he believed that this would destroy the American will to fight. The battleships were therefore the main targets of the attack, but the carrier aviators who planned it regarded the aircraft carriers as the main threat, and allocated a significant number of aircraft against them.

The Japanese plan was inflexible. B5N Kate bombers that could carry either bombs or torpedoes were allocated to one or the other early on in the planning, and their crews were then trained for only one role, making future changes to the bomb/torpedo mix impossible.

The absence of the carriers from Pearl Harbor was known the day before, but no changes were made in the plan, resulting in a large number of torpedoes being wasted on the target ship USS Utah, an unarmed former battleship. Some authors have claimed that the Japanese mistook her for a carrier because her gun turrets had been removed, but Zimm quotes Japanese reports to show that she was attacked in the belief that she was an active battleship.

The attack was unco-ordinated. The bombs of the D3A Val dive bombers could not penetrate battleship armour. They should either have attacked the battleships in the first wave along with the torpedo bombers in order to suppress their AA fire or else bombed cruisers, which they could sink. Instead, the Vals of the second wave wasted many of their bombs on battleships that they could not sink.

The Kate level bombers, which destroyed the USS Arizona, and the attacks on airfields exceeded expectations. However, more ships would have been sunk if more Kates had carried torpedoes, and sinking cruisers was a better use of the Vals’ bombs than destroying aircraft. The Japanese aircrew were badly let down by a large number of dud bombs.

Yamamoto was willing to attack even without the benefit of surprise. Zimm convincingly shows that this would have resulted in very heavy Japanese casualties and much lower American ones.

Zimm characterises Yamamoto as a gambler, who was willing to take big risks. He included midget submarines in the attack. They achieved nothing and risked alerting the Americans. Zimm shows why the theory that a midget submarine torpedoed the Arizona is highly unlikely to be true.

The Americans ought to have had a warning system that would have given them 40 minutes’ warning. Ships would then have had their watertight doors and hatches closed and their AA guns manned, whilst the fighters would have been scrambled. Zimm therefore disagrees with those who try to exonerate General Walter Short and Admiral Husband Kimmel, the US Army and USN commanders.

The attack was a success. The target was to put at least four battleships out of action for a minimum of six months. Yamamoto wanted to destroy at least one battleship, and the Arizona and Oklahoma were lost permanently, but this did not have the psychological effect that he expected. The Nevada was out of service for over six months, and the California and West Virginia did not return to service until 1944, although this delay was partly because they were heavily modernised as well as being repaired. More US aircraft were destroyed than anticipated.

Zimm’s points are that huge risks were taken to achieve this and that a better plan could have inflicted even heavier casualties.

Zimm refutes three well known claims about the battle, which I had accepted until reading his book. The first is that the Japanese should have launched a third strike against shore facilities, including oil tanks. The Navy Yard  was too big to be seriously damaged by the force available. The oil tanks could have been destroyed, but they would have been repaired, and short-term supply shortages could have been met by a re-allocation of Allied tankers. Zimm points out that the Japanese paid little attention to logistics in their planning, so why would they consider disrupting enemy logistics?

He argues that the assertion that there was a heated discussion on whether or not to launch a third strike onboard the Japanese flagship Akagi is a fabrication of Commander Fuchida Mitsuo, the attack leader. Fuchida comes out poorly from this book. Previous research, including this paper by Jonathan Parshall, has doubted his account of the Battle of Midway and his claim to have present at the Japanese surrender in 1945.

The second claim is that it would have been better for the Japanese to meet the Americans at sea. Two of the four battleships that were sunk in the shallow waters of Pearl Harbor were subsequently raised and repaired. They would have been lost if they had suffered the same damage at sea.

Zimm points out that the Japanese would not have scored as many hits on ships that were free to manoeuvre at sea and had their AA guns fully manned. The hits would not have been as devastating on ships that had all their watertight doors and hatches closed.

Comparisons with the sinking of Force Z a couple of days later are invalid. The US ships had better AA systems than the British ones, the US force was larger and the British were attacked by more torpedo bombers than were at Pearl Harbor. At sea, the Japanese could have expected to sink only one US battleship, and then only if they had concentrated their attack on a single ship.

The final claim is that the Japanese aviators were exceptionally well trained and mostly combat veterans. In fact, two of the carriers, Shokaku and Zuikaku, were newly completed, and many of their aircrews were just out of training. Not many of the men on the other four carriers were combat veterans, as carrier aircrews had played relatively little part in the Sino-Japanese War.

The book includes an appendix in which Zimm imagines how the Japanese could have carried out a better attack. More torpedo bombers, better co-ordination and superior target selection result in higher US losses. There is no attempt to extrapolate this into a Japanese victory in the war. It is not one of the counter-factuals, popular on the internet, where one change in weapons production or tactics results in an Axis victory in the Battle of Britain/Stalingrad/Midway and thus the war.

This is an excellent military analysis. It is not a book for everyone. It is not one for anybody who does not know much about the battle or the causes of the Pacific War. It will not appeal to those who dislike acronyms, tables or lots of numbers. There are a number of extracts from memoirs, but these are intended to emphasis points in the analysis, rather than trying to show what it was like to be there.

For those who have some knowledge of the battle, but want a deeper analysis, it is highly recommended.

I read a Kindle copy. The text and quotations were clear, but I would advise e-book readers to switch to landscape format when studying the many maps and tables, which are too small to be legible in portrait format.

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The Fall of Singapore – The Great Betrayal – BBC2

BBC2 recently broadcast a documentary titled The Fall of Singapore – The Great Betrayal. The synopsis from the BBC’s website says that:

Pearl Harbor and the Fall of Singapore: 70 years ago these huge military disasters shook both Britain and America, but they conceal a secret so shocking it has remained hidden ever since. This landmark film by Paul Elston tells the incredible story of how it was the British who gave the Japanese the knowhow to take out Pearl Harbor and capture Singapore. For 19 years before the fall of Singapore to the Japanese, British officers were spying for Japan. Worse still, the Japanese had infiltrated the very heart of the British establishment – through a mole who was a peer of the realm known to Churchill himself.

The main contributors to the programme were Prof. Richard Aldrich of Warwick University, a leading historian of the British intelligence services, and Dr Antony Best of the LSE, an expert on Anglo-Japanese relations. Many of the assertions made were justified by reference to primary documents in the UK National Archives.

At the end of the First World War, the Royal Navy led the world in naval aviation. Japan, which was then allied to Britain, attempted to obtain details of Britain’s new aircraft carriers. Ten requests for information were rejected, but Japan was allowed to recruit a civilian mission.

It was composed of former members of the Royal Naval Air Service, which had merged with the Royal Flying Corps to form the Royal Air Force in April 1918. The mission was led by an experienced naval aviator, William Forbes-Sempill, the Master of Sempill and the son of a Scottish peer. It was in Japan during 1921-23.

The programme argued that the British mission allowed Japan to develop the naval aviation that enabled it to attack Pearl Harbor and to sink Force Z, composed of HMS Prince of Wales and Repulse, off Malaya in December 1941. This is perhaps going too far; Stephen Roskill contended in his history of the RN between the wars that the Japanese would have caught up with the RN and USN eventually, but that the Sempill mission speeded up the process.[1]

The programme suggested that the Japanese needed British help in order to develop naval aviation. They were behind Britain and the USA, but not by as much as the programme suggested. The first deck landing on an aircraft carrier was on HMS Furious on 3 August 1917, which then had a short flight deck forward of her superstructure.

The first carrier with a full length deck was HMS Argus, which was converted from an incomplete liner and completed in September 1918. Britain began construction of the HMS Hermes, the world’s first purpose built carrier, on 15 January 1918. She was launched on 11 September 1919 but not completed until February 1924.

Japan, meanwhile, laid down its first carrier, IMS Hosho, on 16 December 1919. She was launched on 13 November 1921 and completed on 27 December 1922. The first take off from and landing on her deck took place on 22 February 1923. The first landing on a carrier that was underway was on the USS Langley in November 1922. Conversion of the Langley, the USN’s first carrier, from a collier had been completed on 20 March 1922.

The claim made by the programme that the Japanese needed British help to build a carrier would seem to be an exaggeration, since the Hosho was under construction before the Sempill Mission arrived in Japan, but the mission clearly helped the Japanese to develop carrier aviation quicker than they could have managed if starting from scratch.

The second in command of the base from which the mission operated was Yamamoto Isoruku, in 1941 commander of the Japanese Combined Fleet and mastermind of the attack on Pearl Harbor. By 1941 the IJN was well ahead of the RN and at least equal to the USN in carrier aviation, so the Japanese had taken the initial lessons taught to them by the Sempill Mission and built on them by their own efforts. One of Britain’s problems was that most of its naval aviators transferred to the RAF in 1918, so it had few senior officers with air experience in 1939.

Another former RNAS pilot, Frederick Rutland, was recruited by the Mitsubishi company and taught the Japanese deck landing techniques. He was the son of a labourer and was promoted from the ranks. He was known as Rutland of Jutland because he carried out a reconnaissance mission at the Battle of Jutland.

At this stage, Sempill and Rutland had provided an ally with information as part of officially sanctioned missions. The Anglo-Japanese Alliance was ended by the treaties signed at the 1921-22 Washington Naval Conference and the two countries became potential foes. Despite this, Sempill continued to supply information to Japan. He had asecret job that seemed to make him an international arms salesman for Britain. This gave him access to secret information and brought him into contact with foreign navies and air forces, including those of Chile, Brazil and Greece.

MI5 became suspicious of Sempill’s links with Japan and tapped his phone and intercepted his mail. This provided evidence that he was supplying Japan with secret information. Britain had broken some Japanese codes and intercepted Japanese diplomatic cables relaying some of these from London to Tokyo.

In 1926, Sempill visited the Blackburn aircraft factory, ostensibly to inspect a new single-seater aircraft. He managed to obtain plans of the top secret Blackburn Iris flying boat. Soon after this, he was interviewed by the Deputy Chief of the Air Staff, the Director of Public Prosecutions and a senior MI5 officer.

A meeting chaired by Sir Austen Chamberlain, the Foreign Secretary, decided not to prosecute Sempill. His position in society would make this embarrassing, but there was also the perennial problem with espionage cases that it would be hard to convict without revealing secrets, including the fact that Britain had broken Japanese codes. The relevant files are now publicly available in the National Archives, but were kept secret for many years.

There are no MI5 files on Sempill from the 1930s in the National Archives. One from the 1940s states that he was a paid consultant for Mitsubishi in 1931. He needed the money as he was overdrawn by £13,000; nearly £750,00o in 2012 terms.

During the 1930s Sempill became President of the Royal Aeronautical Society and succeeded his father as Lord Sempill, sitting in the House of Lords as a Conservative. He was a member of The Link, an organisation established in 1937 to promote Anglo-German friendship, and The Right Club, which aimed to rid the Conservative Party of Jewish influence.

Whether or not Sempill was involved, Japanese espionage against Britain continued during the 1930s. In 1931, Japan invaded Manchuria. This raised fears of an Angl0-Japanese war, and Britain re-started work on a large naval base at Singapore. The programme suggested that construction began in 1931; in fact, building started in 1923 but was suspended more than once during the 1920s due to changes in government and budgetary constraints.

During the 1930s Japanese businessmen bought up large amounts of property in Malaya. The programme argued that many of them were spies. Japan bought the plans for the Singapore base from a British serviceman called Roberts.

The Singapore base was heavily defended against attack from the sea. The British thought that it would be impossible to invade Malaya and then attack Singapore by land. In 1937 Joe Vinden (spelling?), a British Army intelligence officer, reconnoitred the Malayan coast and concluded that an invasion of Malaya followed by a land attack on Singapore was feasible.

Vinden correctly forecast that the Japanese would land at Kota Bharu in north-east Malaya during the November-February monsoon season; others thought that an amphibious landing at that time of year was impossible. His recommendation that funds allocated to coastal artillery be instead spent on aircraft was ignored.

Japan also had spies in Hawaii, one of whom was Rutland. He later told interrogators that he was ordered to report on the attitude of the population to the possibility of war and on the dispositions of the US fleet. The FBI soon became suspicious of his activities.

Sempill was brought back to the Admiralty when Winston Churchill was appointed First Lord of the Admiralty, the cabinet minister responsible for the navy, on the outbreak of war in 1939. Sempill gave an assurance that he would not discuss service matters with the Japanese. However, in August 1941 he intervened to secure the release of Satoru Makahara, manager of Mitsubishi’s London office, who had been arrested on suspicion of espionage.

At the same time Churchill and US President Roosevelt held secret talks at Placentia Bay. Shortly afterwards the British code breakers at Bletchley Park intercepted and decoded a signal from the Japanese Embassy in London to Tokyo that gave precise details of the talks. A report that was sent to Churchill about the intercept remained secret for 60 years; he noted that the Japanese version was ‘pretty accurate stuff.’ It had to have come from somebody close to him.

Richard Aldrich said that the most important Japanese source with access to Churchill was Sempill. A few days later MI5 told Churchill that the Japanese had information about his inner circle. He demanded proof and a month long surveillance operation produced the names of Sempill and Commander McGrath, who had been with Sempill in Japan.

Churchill stated that Sempill could not remain at the Admiralty. When Sempill was asked to resign his commission, however, Churchill said that he only wanted Sempill to leave his current job, not the RN. Antony Best pointed Sempill was a Conservative peer who would have had friends in the Conservative Party. Richard Aldrich argued that interning Sempill would look very bad for the government, which had employed him even though he had been under MI5 surveillance since 1925.

Rutland was deported to Britain by the Americans and interned. He was released near the end of the war and later committed suicide. Sempill was given a choice of either resigning his commission or taking up a post in northern Scotland; the programme did not make it clear that which he chose. He died in 1965.

It was argued that Sempill was not charged under the Official Secrets Act or interned under Defence Regulation 18B because he was a well connected aristocrat and his arrest would embarrass the government. Other members of the upper classes were interned, including Sir Oswald Moseley, founder of the British Union of Fascists and his wife Diana, one of the Mitford sisters, Admiral Sir Barry Domvile and Archibald Maule Ramsay, the Conservative MP who founded The Right Club.

However, none of them had held any government position during the war, whilst Sempill was close to the Prime Minister. This would suggest that embarrassment to the government in general and Churchill in particular for appointing a man previously suspected of supplying secrets to Japan to a sensitive post was a stronger reason for not taking action against him than his social position.

Another reason might be that a trial could have revealed that the British had broken Japanese codes. The programme mentioned this when discussing why he was not charged in 1925, but did not repeat the point when discussing his lack of punishment in 1941.

This was a very interesting programme. It should be noted that it was not as new a revelation as the BBC claimed. The relevant documents were released to public view at the National Archives in 1998, and The Independent newspaper reported on them, quoting Richard Aldrich. Nevertheless, the programme was well made, justified its claims with reference to primary documents and brought the story to a wider audience.


[1] Stephen Roskill, Naval Policy Between the Wars, vol. i (London: Collin, 1968), p. 529.

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