―― 空襲警報から爆撃までの時間は、もっとも楽観的な数値で"5.3分" (by フェルミ推定)


There is a heavy snowfall warning for the entire Kanto area.


Recently, there have been frequent warnings of typhoons, heavy rains, and guerrilla torrential rains.

しかも、かなり正確です ―― 年々精度が向上しているように思います。

And it's pretty accurate -- it seems to be getting more accurate every year.


I remember that I once did some research on how to forecast the weather, and I had the impression that 'this is difficult.


I'm not sure what kind of forecasting method they are using now, but I think they are basically using information from weather sensors set up all over the country and running supercomputers in real time.


However, miss predictions happen.


The JMA's excuse ... or explanation ... can be found here.



Nevertheless, weather forecasting can be done by using information from each base (temperature, pressure, and other current weather information) to calculate the equations of physics by force.


Then I wondered how they did "air raid warnings" during the Pacific War.

頭上から、爆弾が投下されるという危機 ―― これは、雪や台風などとは比較にならない、生命に直結する情報です。

The danger of a bomb being dropped from overhead. This information is much more life-threatening than that of snow or typhoons.


I don't have to tell you how important this is.


(You will hear an air raid alarm.)

調べてみたとろ、(1)レーダー、(2)目視(at 監視哨)、(3)音(by 聴音機) の3つを使っていたようです。

I found out that they were using (1) radar, (2) visual (at watchtowers), and (3) sound (by listening devices).


Radar, which "emits microwaves and observes the reflected waves," was able to detect bombers up to 100 kilometers away even back then.


However, it was only just before the end of the war (1944) that experiments for practical use were successful, and the accuracy was poor, making mass production difficult.


Also, it seems that the Japanese military (especially the navy) was reluctant to develop radar because it would 'only let the enemy know their position.


More than that, it seems that the people of our country had little awareness of "air raids".


In the first place, the period of air raids was quite short compared to the entire duration of the war (about four years).


Based on Japan lost the war on August 15, 1945, I calculated that one year is 1.0.

一番最初の那覇空襲が1944年10月10日で"-0.85", 鹿児島空襲が、"-0.41",倉敷空襲が"-0.32"で、その後、"-0.12"(50日前)からは、ほぼ、毎日、日本各地で爆撃が続けれらていました。

The first air raid on Naha was on October 10, 1944, with a -0.85, the first air raid on Kagoshima was -0.41, the first air raid on Kurashiki was -0.32, and after that, from -0.12 (50 days ago), bombings continued almost every day all over Japan.


There were only a handful of radars installed in Japan (probably only in the imperial capital (Tokyo)) to counter enemy attacks that could appear anywhere.


"Air raid alerts" that rely only on our eyes and ears.


If there was a 15-meter high watchtower, the logical visibility distance was 15 kilometers.


In addition, let's assume that they had human eyesight plus binoculars, and that they were blessed with extremely good weather, and that half of this distance, about 7 km, was the distance at which they could detect enemy aircraft.

戦闘機の巡航速度が200kmとして ―― 敵機発見は、126秒前です。

Assuming the fighter's cruising speed is 200 kilometers -- the enemy plane was spotted 126 seconds ago.


Even if they estimated that the alert procedure took one minute, and the arrival time at the destination was three times that time.

―― 空襲警報から爆撃までの時間は、もっとも楽観的な数値で"5.3分" (by フェルミ推定)

"The most optimistic figure for the time between air raid warning and bombing is 5.3 minutes(by Fermi)."


Including preparation, the distance a person can escape in "five minutes" is probably less than one kilometer.


Of course, this is much longer than the "few seconds" of the current Earthquake Early Warning System.


They might have been able to buy enough time to escape to the air-raid shelter, but if a bomb hit us, they would have no chance of survival.


Even so, when the "air raid alarm" was issued, actions such as "turn off the lights" and "escape to an air-raid shelter" were well known to all.


Nowadays, there is a system called the National Instantaneous Warning System (J-Alert), but frankly speaking, I didn't know what action to take, so I did some research.


I will keep this in mind as it was mentioned here.



In any case, I am grateful for the "alert".


gain, I would like to express my gratitude to everyone involved in the design, construction, and operation of "alarm system".


Posted by ebata