Curtis Emerson LeMay (November 15, 1906 – October 1, 1990) was a Major General in the United States Air Force during the WWII.

Robert McNamara described LeMay's character, in a discussion of a report into high abort rates in bomber missions during World War II:

One of the commanders was Curtis LeMay—Colonel in command of a B-24 [sic] group. He was the finest combat commander of any service I came across in war. But he was extraordinarily belligerent, many thought brutal. He got the report. He issued an order. He said, 'I will be in the lead plane on every mission. Any plane that takes off will go over the target, or the crew will be court-martialed.' The abort rate dropped overnight. Now that's the kind of commander he was.[12]

In August 1944, LeMay transferred to the China-Burma-India theater and directed first the XX Bomber Command in China and then the XXI Bomber Command in the Pacific. LeMay was later placed in charge of all strategic air operations against the Japanese home islands.[9][10]

LeMay soon concluded that the techniques and tactics developed for use in Europe against the Luftwaffe were unsuitable against Japan. His Boeing B-29 Superfortress bombers flying from China were dropping their bombs near their targets only 5% of the time. Operational losses of aircraft and crews were unacceptably high owing to Japanese daylight air defenses and continuing mechanical problems with the B-29. In January 1945, LeMay was transferred from China to relieve Brigadier General Haywood S. Hansell as commander of the XXI Bomber Command in the Marianas.[9][10]

He became convinced that high-altitude precision bombing would be ineffective, given the usually cloudy weather over Japan. Furthermore, bombs dropped from the B-29s at high altitude (20,000+ feet) were often blown off of their trajectories by a consistently powerful jet stream over the Japanese home islands, which dramatically reduced the effectiveness of the high-altitude raids. Because Japanese air defenses made daytime bombing below jet stream-affected altitudes too perilous, LeMay finally switched to low-altitude nighttime incendiary attacks on Japanese targets, a tactic senior commanders had been advocating for some time.[9][10] Japanese cities were largely constructed of combustible materials such as wood and paper. Precision high-altitude daylight bombing was ordered to proceed only when weather permitted or when specific critical targets were not vulnerable to area bombing. General LeMay was informed by a senior staff member, Colonel William P. Fisher, that bomber pilots were turning back from these low altitude bombing runs due to heavy anti-aircraft fire from Japanese defense forces. Fisher suggested to LeMay that crews who achieved successful strike rates should be rewarded by being released from their deployment. LeMay implemented this unorthodox plan and the strike rate went up to eighty percent.[13]

LeMay commanded subsequent B-29 Superfortress combat operations against Japan, including massive incendiary attacks on 67 Japanese cities. This included the firebombing of Tokyo — known in official documents as the "Operation Meetinghouse" air raid on the night of March 9–10, 1945 — which proved to be the single most destructive bombing raid of the war.[14] For this first attack, LeMay ordered the defensive guns removed from 325 B-29s, loaded each plane with Model M-47 incendiary clusters, magnesium bombs, white phosphorus bombs, and napalm, and ordered the bombers to fly in streams at 5,000 to 9,000 feet (1,500 to 2,700 m) over Tokyo.[9][10][15]

Precise figures are not available, but the firebombing campaign against Japan, directed by LeMay between March 1945 and the Japanese surrender in August 1945, may have killed more than 500,000 Japanese civilians and left five million homeless.[17] Official estimates from the United States Strategic Bombing Survey put the figures at 220,000 people killed.[14] Some 40% of the built-up areas of 66 cities were destroyed, including much of Japan's war industry.[14][18]

LeMay was aware of the implication of his orders. The New York Times reported at the time, "Maj. Gen. Curtis E. LeMay, commander of the B-29s of the entire Marianas area, declared that if the war is shortened by a single day, the attack will have served its purpose."[9][10] The argument was that it was his duty to carry out the attacks in order to end the war as quickly as possible, sparing further loss of life. He also remarked that had the U.S. lost the war, he fully expected to be tried for war crimes.

Throughout history (perhaps up to and including WWII), I would say that megalomania has been the essential personality trait (disorder ?) of a successful general (I am not too sure about whether narcissism was more helpful or hurtful ... perhaps depends on the culture ?) ... HOWEVER nowadays (after the advent of nuclear weapons), having  military commanders with megalomaniacal tendencies is likely a very dangerous thing for the posterity of humankind (not to mention the rest of the life on this planet).

Curtis Emerson LeMay (November 15, 1906 – October 1, 1990) was a Major General in the United States Air Force during the WWII.

Robert McNamara described LeMay's character, in a discussion of a report into high abort rates in bomber missions during World War II:

One of the commanders was Curtis LeMay—Colonel in command of a B-24 [sic] group. He was the finest combat commander of any service I came across in war. But he was extraordinarily belligerent, many thought brutal. He got the report. He issued an order. He said, 'I will be in the lead plane on every mission. Any plane that takes off will go over the target, or the crew will be court-martialed.' The abort rate dropped overnight. Now that's the kind of commander he was.[12]

In August 1944, LeMay transferred to the China-Burma-India theater and directed first the XX Bomber Command in China and then the XXI Bomber Command in the Pacific. LeMay was later placed in charge of all strategic air operations against the Japanese home islands.[9][10]

LeMay soon concluded that the techniques and tactics developed for use in Europe against the Luftwaffe were unsuitable against Japan. His Boeing B-29 Superfortress bombers flying from China were dropping their bombs near their targets only 5% of the time. Operational losses of aircraft and crews were unacceptably high owing to Japanese daylight air defenses and continuing mechanical problems with the B-29. In January 1945, LeMay was transferred from China to relieve Brigadier General Haywood S. Hansell as commander of the XXI Bomber Command in the Marianas.[9][10]

He became convinced that high-altitude precision bombing would be ineffective, given the usually cloudy weather over Japan. Furthermore, bombs dropped from the B-29s at high altitude (20,000+ feet) were often blown off of their trajectories by a consistently powerful jet stream over the Japanese home islands, which dramatically reduced the effectiveness of the high-altitude raids. Because Japanese air defenses made daytime bombing below jet stream-affected altitudes too perilous, LeMay finally switched to low-altitude nighttime incendiary attacks on Japanese targets, a tactic senior commanders had been advocating for some time.[9][10] Japanese cities were largely constructed of combustible materials such as wood and paper. Precision high-altitude daylight bombing was ordered to proceed only when weather permitted or when specific critical targets were not vulnerable to area bombing. General LeMay was informed by a senior staff member, Colonel William P. Fisher, that bomber pilots were turning back from these low altitude bombing runs due to heavy anti-aircraft fire from Japanese defense forces. Fisher suggested to LeMay that crews who achieved successful strike rates should be rewarded by being released from their deployment. LeMay implemented this unorthodox plan and the strike rate went up to eighty percent.[13]

LeMay commanded subsequent B-29 Superfortress combat operations against Japan, including massive incendiary attacks on 67 Japanese cities. This included the firebombing of Tokyo — known in official documents as the "Operation Meetinghouse" air raid on the night of March 9–10, 1945 — which proved to be the single most destructive bombing raid of the war.[14] For this first attack, LeMay ordered the defensive guns removed from 325 B-29s, loaded each plane with Model M-47 incendiary clusters, magnesium bombs, white phosphorus bombs, and napalm, and ordered the bombers to fly in streams at 5,000 to 9,000 feet (1,500 to 2,700 m) over Tokyo.[9][10][15]

Precise figures are not available, but the firebombing campaign against Japan, directed by LeMay between March 1945 and the Japanese surrender in August 1945, may have killed more than 500,000 Japanese civilians and left five million homeless.[17] Official estimates from the United States Strategic Bombing Survey put the figures at 220,000 people killed.[14] Some 40% of the built-up areas of 66 cities were destroyed, including much of Japan's war industry.[14][18]

LeMay was aware of the implication of his orders. The New York Times reported at the time, "Maj. Gen. Curtis E. LeMay, commander of the B-29s of the entire Marianas area, declared that if the war is shortened by a single day, the attack will have served its purpose."[9][10] The argument was that it was his duty to carry out the attacks in order to end the war as quickly as possible, sparing further loss of life. He also remarked that had the U.S. lost the war, he fully expected to be tried for war crimes.

Henry VIII was every bit the tyrant and monster that Ivan IV (the terrible) was in Russia a generation later.  

He can join a long list of 'English' heroes who also have rather a larger dark side than their shining light.  To name but a few...

Richard Coeur de Lion (massacred thousands of prisoners and abandoned his kingdom)

Henry VII (usurper and founder of the Tudors, the bloodiest dynasty in English history) 

Cromwell (regicide, military dictator who ravaged Ireland in an anti-catholic purge)

Queen Victoria  Imperialist and despot even to her own children many of whom were also psychologically damaged) 

We cannot of course judge historical characters by 21st century morals but we also cannot lionise people by 19th century values as the British do rather often.

It should perhaps be noted that Ivan IV is more often referred to as Ivan the Great rather than the 'Terrible' in Russia.  perhaps the difference between megalomania and narcissism and greatness and heroic status is merely nationalism.

Narcissism is not good traits in a military command, because it prevents to evaluate cases-in conditions- features in a different ways or multidirectional approaches. Narcissism has made up a blind brain. Every army has to avoided to have  a narcissistic person as a commander. 

Winston Churchill, another historical giant and undoubted megalomaniac/narcissist was the great war leader who brought Britain through its 'darkest hour'.  

Churchill displayed almost histrionic narcissism during his early career and engaged in schemes of destructive grandiosity.  During the years of hubris between the wars he  suffered severe depression which he referred to as his 'black dog'.

It is almost impossible to criticise Churchill without being screamed down by 'patriots' in spite of his catastrophic actions such as Gallipoli and his attacks on the working classes.  

There is no doubt that Churchill was instrumental in the destruction of Nazism and that as a war leader his megalomania was productive in many ways.  That does not mean however that we should gloss over his many severe shortcomings.

It is perhaps most telling that in the first election following the end of WW2 the electorate rejected him as the leader for peacetime.  

I agree, this is a very negative trait, but the history knows examples when commanders were far from megalomania. For example, Suvorov ( https://en.wikipedia.org/wiki/Alexander_Suvorov ) who was a very humble man, and his life went in circles: "his country estate - an Empress's order - military expedition - country life - a new order..." Was Empress Catherine the Great "magalomaniac"? - it's another question. But it's clear, if she wasn't, her state would become a part of Turkey, Prussia, Britain or anything else, that were, in their turn, under other crowned "megalomaniacs" :-). 

Qin Shi Huang, who died on Sept. 10, 210 B.C., after conquering six warring states to create the first unified nation of China.  Without this megalomaniac: no Chineese empire which is the most enduring empire in history.  

A single look at his tomb give us a small glimpse to his megalomania. More than 700,000 workers were involved in its construction under incredible bad working conditions.  Workers were organised in small working units and the workers with the smallest production were systematically killed.

One of his many megomaniac obsession was overcoming death:

''Towards the end of his life, Qin Shi Huang became obsessed with finding an elixir that would make him immortal. He eventually died during a tour of eastern China in 210BCE after swallowing mercury pills which his advisers believed would give him everlasting life.''

''The military might of the Qin was matched only by its brutality. One famous general, called Bai Qi, is reputed to have killed more than a million soldiers and seized more than 70 cities. In 278BCE, he led the Qin army to victory against its biggest rival from the Yangtze south, the Chu. He then went on to defeat the Zhou, the nominal kings of China, at the Battle of Changping in 260BCE. After this battle he had more than 400,000 prisoners of war slaughtered by burying them alive.''