The regional city of Shizuoka after being firebombed on June 18, 1945. Photo by Hidenori Watanave.

The summer months are a time of reflection in Japan. Each August marks O-Bon, the annual festival of the dead, when deceased relatives are said to visit their ancestral homes mid-month before returning to the netherworld. August is also the anniversary of the atomic bombings of Hiroshima and Nagasaki, as well as Japan's capitulation in 1945 and the end of the Second World War.

The bombing of Hiroshima, and, to a lesser extent, Nagasaki, which resulted in the destruction of both cities and hundreds of thousands of dead, is well known outside of Japan. What is not as well known is the methodical firebombing campaign in the months that lead up to the deployment of nuclear weapons and the end of the war that destroyed nearly all of Japan's cities.

Starting with the firebombing of Tokyo in March 1945 — the single-most destructive air raid of the war –bombing raids systematically targeted Japan's cities for complete and utter destruction in June and July 1945. Japanese researcher Hidenori Watanave, who specializes in online mapping technology, has posted colorized images of the bombings on Twitter.

72年前の今日。1945年6月22日，姫路空襲。9時50分ごろB-29約60機が飛来し，川西航空機姫路製作所を中心に約1時間の爆撃を行なった。死者341人，被災者10220人。ニューラルネットワークによる自動色付け。 pic.twitter.com/3hhreqYyty

— Hidenori Watanave (@hwtnv) June 21, 2017

On this day, 72 years ago: on June 22, 1945, the great Himeji Air Raid occurred. At about 9:50, 60 B-29 bombers appeared, targeting the Kawanishi airplane factory in Himjeji for about an hour with bombs. 341 people died, and 10,220 were left homeless. Image colorized by neural network.

Watanave uses a web-based tool to add color to black-and-white images, and often researches the images of the bombing on JapanAirRaids.org, a digital archive dedicated to the international dissemination of information about the air raids conducted by the United States Army Air Forces and Navy against Japan.

‘Tokyo – the the morning after!’ Source: Library of Congress, Curtis LeMay Papers, Air Intelligence Report, Vol. 1, No. 2. and Journal of Historical Geography, ‘A cartographic fade to black: mapping the destruction of urban Japan during World War II.‘

The methodical destruction of Japan's cities is estimated to have resulted in 333,000 killed and 473,000 wounded civilians, with an estimated 15 million left homeless.

72年前の今日。1945年6月22日の朝，呉軍港空襲。162機のB29が合計1289発の爆弾を投下。「この世界の片隅に」の晴美は，この空襲で投下された時限爆弾によって亡くなった。ニューラルネットワークによる自動色付け。 pic.twitter.com/IXyZzM3dy3

— Hidenori Watanave (@hwtnv) June 21, 2017

On this day, 72 years ago: in the morning of June 22, 1945, the Kure Naval Yard air raid occurred. 162 B-29 bombers dropped a total of 1,289 bombs on the facility. Harumi, a character in the [2016] animated film ‘In This Corner of the World‘, was killed by a delayed-release bomb in this air raid.

72年前の今日。空襲を受ける呉軍港。ニューラルネットワークによる自動色付け。 pic.twitter.com/Nk77XvsdgE

— Hidenori Watanave (@hwtnv) June 21, 2017

72 years ago today: Kure under attack.

空襲後の呉軍港。ニューラルネットワークによる自動色付け。 pic.twitter.com/Mn1DkzscAP

— Hidenori Watanave (@hwtnv) June 21, 2017

The port of Kure, following the air raid.

72年前の今日，空襲で炎上する静岡市街。ニューラルネットワークによる自動色付け。 pic.twitter.com/Aua7m8bDXF

— Hidenori Watanave (@hwtnv) June 18, 2017

72 years ago today: Shizuoka burns during an air raid.

72年前の今日。静岡大空襲。1945年6月19日深夜から20日未明にかけて，B-29爆撃機137機により旧静岡市市街が攻撃された。死者1,952名以上，負傷者5,000名以上，焼失戸数26,891戸。ニューラルネットワークによる自動色付け。 pic.twitter.com/ftyy4yZojd

— Hidenori Watanave (@hwtnv) June 18, 2017

72 years ago today: the Great Shizuoka Air Raid. Late at night on June 19 until the early morning hours of June 20, 137 B-29 bombers attacked what was the city center of Shizuoka. 1,952 died, and more than 5,000 were injured. 26,891 homes were destroyed by fire.

72年前の今日。福岡大空襲。1945年6月19日から翌6月20日にかけて，福岡県福岡市の市街地が攻撃された。この空襲により，1,000人以上が死亡・行方不明となった。ニューラルネットワークによる自動色付け。 pic.twitter.com/s5oGixFjv5

— Hidenori Watanave (@hwtnv) June 18, 2017

On this day, 72 years ago: the Great Fukuoka Air Raid occurred on June 19 and June 20 when Fukuoka City center was attacked. This air resulted in more than 1,000 dead and missing.

72年前の今日。1945年6月18日，浜松と四日市が空襲を受けた。浜松では死者1720人・焼失家屋15,400戸，四日市では死者736人・負傷者1500名・行方不明63人・被災者47,153名・焼失家屋11,390戸。写真は浜松。ニューラルネットワークによる自動色付け。 pic.twitter.com/lZnoeRgTEy

— Hidenori Watanave (@hwtnv) June 18, 2017

On this day, 72 years ago: Hamamatsu (in Shizuoka Prefecture) and Yokkaichi (in nearby Mie) were bombed. In Hamamatsu, 1,720 people were killed, and 15,400 houses destroyed. In Yokkaichi, 736 people died, 1,500 were injured and 63 went missing. The number of displaced was 47,153 and the number of houses destroyed was 11,390. This photograph is of Hamamatsu.

72年前の今日，空襲を受けて破壊された浜松市街。ニューラルネットワークによる自動色付け。 pic.twitter.com/VjECGpBHgc

— Hidenori Watanave (@hwtnv) June 18, 2017

72 years ago today, the center of Hamamatsu was destroyed after being bombed.

72年前の今日。1945年6月17日，鹿児島大空襲。鹿児島市内一円が焼夷弾により爆撃され，死者2,316人、負傷者3,500人を出した。ニューラルネットワークによる自動色付け。 pic.twitter.com/ILUNhIFcrW

— Hidenori Watanave (@hwtnv) June 16, 2017

72 years ago today: on June 17, 1945, the Great Kagoshima Air Raid occurred. The entire city was targeted with incendiary bombs, leaving 2,316 dead and 3,500 injured.

爆撃を受ける鹿児島・垂水の街。ニューラルネットワークによる自動色付け。 pic.twitter.com/huVrro8xHA

— Hidenori Watanave (@hwtnv) June 16, 2017

Bombed-out Kagoshima and neighboring Taramizu.

To colorize the images, Watanave has relied on a Waseda University online project called Neural Network-based Automatic Image Colorization. Neural networks are computer systems that work in a way that's similar to the human brain. 

Watanave has used the tool in several projects devoted to preserving and mapping eyewitness testimony from World War II, including an interactive map of the Hiroshima and Nagasaki atomic bombings, and the Battle of Okinawa in 1945. Watanave is also the creator of a similar innovative mapping project that tracks the last moments of the victims of the March 2011 earthquake and tsunami in Japan.

Anyone can use Waseda University's neural network-based automatic image colorization tool here.