Japan were involved, to a large degree, in devoloping biological weapons.

A wonderful little gentlman called 'Ishi' was responsible for the setting up of a large complex in Manchuria, where all sorts of biological agents were created and experimented with, much to the discomfort of the local population. Not the least of which was Bubonic Plague.
Some US prisoners were actually taken there and 'experimented' on.

Bubonic Plague was dropped on an entire toen in Manchuria, to test it's effectiveness. It worked! 

He was also involved in 'delivery' systems for the agents.
They included conventional bombs (which were unsatisfactory because the majority of the pathogen was destroyed in the blast). They made 'ceramic' type bombs that exploded above the ground with a minimum charge, but the wind caused the spread to be unpredictable.

The had quite ingenious little balloons (made of rice paper) that carried incenidaries and conventional explosives across the Pacific (by way of the natural wind currents) and many reached the US and some Forest fires were started. (The purpose was to set fire to large areas of the western forests in the US and disrupt the 'vital' timber industry.
The Japanese concluded that the ballons were unreliable and hardly any were making it, but many were, but the Government kept it quiet so as not to panic the population. The Japanese took the lack of publicity as evidence that none had reached the forests. They thought that if any had, the 'American Press' would have made big news of it and they would have heard.

It's assumed that this is why the biological agents wern't delivered (or at least attempted) by this method. Although, had the Japanese known the ballons were relatively effective, they would certainly have used them.

Our friend Ishi, bought his life and freedom by agreeing to supply all his drawings and plans for his 'ingenious' devices and pathogens to the US Government and working for them! The US Government were apparently more fearful of what the Russians might be getting up to and 'countering' it, than punishing a man responsible for 'untold' inhuman acts and suffering.
As they say in the US.........Go figure?   

'The Destruction of Dresden' by David Irving (a little pro-Axis bias but a good read nonetheless) suggests that US and British air forces developed a combination of conventional high explosives and incendiaries that, in properly combined amounts and timing, created the effect known as the firestorm.

Mr. Irving suggests that the Allies experimented with this technique in Europe to the point where it had more destructive power than the atomic bomb and would have been used to a greater extent in Japan but for the development of the atomic bomb.  Apparently the terror factor of a single bomb was greater than several, more highly destructive bombs.

As a result the death toll (Mr. Irving's figures) in Dresden was 135,000.  In Hiroshima (Mr. Irving's figures) it was 72,000.

Another perhaps more interesting book/movie regarding Dresden is "Slaughterhouse Five' by Kurt Vonnegut, Jr., who actually lived through the bombing as as POW.

I am not now nor have I ever been a fan of Mr. Irving.  The discussion concerned WWII weapons of mass destruction, of which the firestorm was a part.

Mr. Irving's theory, and I believe I adequately indicated that it was Mr. Irvings' theory, was that early Nazi bombings of Rotterdam, among others, accidentally created firestorms.  Seeing that the effects of high explosives combined with incendiaries multiplied the effects of both the Allies (and in particular, Mr. Irving's greatest political enemy, Winston Churchill) experimented with and intentionally caused further firestorms in cities such as Hamburg and Dresden.

If one were to read the entire book Mr. Irving's biases would be obvious.  He believes Winston Churchill's war strategy was to kill as many civilians as possible and let the Russians worry about the soldiers.

Politics aside, and the politics of this book are so obvious that they are easy to ignore, firestorms did happen, in both Allied and Axis territories, including Japan.

From an aviation point of view, bombing missions are described in great detail and include discussions of early loran, chaff and radar technology.

Perhaps I have given 605 Scorpion a subject which he can research for school and give us a further report on.

None taken.  I place Mr. Irving on a par with Eric Von Daniken.

This particular book is well researched and interesting reading.  The author's political views and personal opinions mar an otherwise accurate and detailed historical account.

Slaughterhouse Five, on the other hand, is a great science fiction novel/movie based in part on the author's experience.  If Kurt Vonnegut has bizzare political views, and he probably does, I couldn't care less.  I've read just about everything he's ever written.

That's kind of like the joke about why a dog licks himself.  Because he can.  Nazi bombings accidentally created the first firestorms.  To exploit that discovery they needed the ability to re-create it.  Since they occupied western Europe there was nothing there for them to bomb and after the Battle of Britain they never got close to bombing England.  Spain, maybe, but I don't recall reading about any firestorms there.

The Allies were bombing Germany and occupied Europe as early as 1943, with effectiveness increasing over time.  By 1944 the Allies had overwhelming air superiority and, if you believe the worst, could experiment with the firestorm phenomena in Germany as practice for Japan.  In the 1940's a lot of buildings in Germany were made of wood.

If you were inclined to intentionally create a firestorm you would drop high explosives which would explode at rooftop level, blowing the buildings apart and creating a few small fires.  For maximum effect (according to Mr. Irving, and I believe he is correct on most of this) you would wait a couple of hours for the defending fighters to return to base, the civilians to come out of their bomb shelters, and the local firefighters to go into action.  You would then follow up with incendiaries which would catch the fighters off gaurd and the civilians in the open, and set fire to all the lumber.  You would have to do this on a massive scale to create a huge fire which, in order to sustain itself, draws in huge amounts of air (compare the draft created in a fireplace).

In scale the winds created are hurricane force, drawing in anything not permanently fixed to the ground and sucking it up into an updraft.  A bomb shelter would not offer protection because inhabitants would either suffocate or die from the heat.

The nature of total war, unfortunately, dictates that civilians will die.  Allied war strategy, I like to believe, was first, kill soldiers in battle, then destroy the enemy's ability to make war by destroying his factories, transportation, infrastructure, etc. and, if necessary, destroy his workers' ability to work by destroying their homes with the side effect of demoralization.  Subsequent wars have proven that civilian attacks do not produce either of these effects.

Soviet weapons are a whole 'nother thing.  Whatever they had they weren't and probably still aren't telling anyone.  Archives are opening up every day.  I can recommend a good video series I saw many years ago on PBS called 'The Forgotten War' about how the Soviet Union singlehandedly won WWII.  When you look at the credits you can see it was produced by, guess who, the Soviet Union.  Still, it was pretty good.

WWII is fascinating on so many levels.  Roots in the Versailles Treaty, the rise of Hitler and Nazism, appeasement, blitzkrieg; battles of Britain, France, Stalingrad (my personal favorite - Russia still refuses to release its death toll, estimated at 1 million), the Bulge; technology; brilliant and bungled military strategies; the plots to kill Hitler ...

Back to the original question WMD should certainly include the heavy bomber, which made large scale attacks with conventional weapons possible.  Tanks were biggies but they were fortunately usually addressed towards military targets (other tanks) and weren't really "mass" destruction unless you got a few hundred of them together.

Then we had better not discuss the "humane" full metal jacket.

Here's a webpage on the Japanese Biological Unit I spoke of - Unit 731.
(There were also other Units involved in both Biological and Chemical (gases) research and manufacture).
http://www.skycitygallery.com/japan/japan.html#unit731

"The Other Holocaust"

The research program was one of the great secrets of Japan during and after World War II : a vast project to develop weapons of biological warfare including following deadly diseases :

Bubonic Plague, Anthrax (including inhalation,
skin and gastrointestinal types),
Smallpox, Typhoid,
Paratyphoid A and B, Tularemia,
Cholera Epidemic, Hemorrhagic Fever,
Syphilis, Aerosols,
Botulism, Brucellosis,
Dysentery, Tetanus,
Glanders, Tuberculosis,
Yellow feve,r Typhus,
Tularemia, Gas Gangrene,
Scarlet Fever, Songo,
Diphtheria, Brysipelas,
Selmonella, Venereal Diseases
Infectious Jaundice Undulant Fever
Epidemic Cerebrospinal Meningitis, Tick Encephalitis,
Plant diseases for crop destruction, Dozen other pathogens

Unit 731 & Unit 100 were comprised of over 3,000 researchers and technicians. It was a gigantic research center focused on biological weapons - the world's most technically advanced at the time, used human as the guinea pigs, known as marutas (logs). The Japanese told the locals that the facilities were lumber mills.

The Ping Fan facility alone could monthly "manufacture as much as 300 kg of plague bacteria... 500-600 kg of anthrax germs, 800-900 kg typhoid, paratyphoid, or dysentery germs, or as much as 1000 kg of cholera germs." If several different diseases were manufactured simultaneously, then the total production of pathogens could be many times higher.

A former member of Unit 731 testified that "to eliminate any chance of leaking out the secret of construction of the 'Square Buildings' by the laborers, they are all sent to special prison and used as the first batch of test objects."

More than 10,000 Chinese, Korean and Russian PoWs were slaughtered in these biological experiments