World would be observing Hiroshima day today, 65 years after American bombers dropped deadly bombs in the Japan city. UN secretary general Banki-Moon would be attending the Remembrance Day function in Hiroshima.

In the early morning hours of August 6, 1945, a B-29 bomber named Enola Gay took off from the island of Tinian and headed north by northwest toward Japan. The bomber’s primary target was the city of Hiroshima, located on the deltas of southwestern Honshu Island facing the Inland Sea. Hiroshima had a civilian population of almost 300,000 and was an important military center, containing about 43,000 soldiers.

The bomber, piloted by the commander of the 509th Composite Group, Colonel Paul Tibbets, flew at low altitude on automatic pilot before climbing to 31,000 feet as it neared the target area. At approximately 8:15 a.m. Hiroshima time the Enola Gay released “Little Boy,” its 9,700-pound uranium bomb, over the city.

Hiroshima during World War II

At the time of its bombing, Hiroshima was a city of some industrial and military significance. A number of military camps were located nearby, including the headquarters of the Fifth Division and Field Marshal Shunroku Hata’s 2nd General Army Headquarters, which commanded the defense of all of southern Japan. Hiroshima was a minor supply and logistics base for the Japanese military. The city was a communications center, a storage point, and an assembly area for troops. It was one of several Japanese cities left deliberately untouched by American bombing, allowing a pristine environment to measure the damage caused by the atomic bomb.

The center of the city contained several reinforced concrete buildings and lighter structures. Outside the center, the area was congested by a dense collection of small wooden workshops set among Japanese houses. A few larger industrial plants lay near the outskirts of the city. The houses were constructed of wood with tile roofs, and many of the industrial buildings were also built around wood frames. The city as a whole was highly susceptible to fire damage.

The population of Hiroshima had reached a peak of over 381,000 earlier in the war, but prior to the atomic bombing the population had steadily decreased because of a systematic evacuation ordered by the Japanese government. At the time of the attack the population was approximately 340,000-350,000. Because official documents were burned, the exact population is uncertain.

The bombing

Hiroshima was the primary target of the first nuclear bombing mission on August 6, with Kokura and Nagasaki being alternative targets. August 6 was chosen because clouds had previously obscured the target.

The 393d Bombardment Squadron B-29 Enola Gay, piloted and commanded by 509th Composite Group commander Colonel Paul Tibbets, was launched from North Field airbase on Tinian in the West Pacific, about six hours flight time from Japan. The Enola Gay (named after Colonel Tibbets’ mother) was accompanied by two other B29s. The Great Artiste, commanded by Major Charles W. Sweeney, carried instrumentation; and a then-nameless aircraft later called Necessary Evil (the photography aircraft) was commanded by Captain George Marquardt.

After leaving Tinian the aircraft made their way separately to Iwo Jima where they rendezvoused at 2,440 metres (8,000 ft) and set course for Japan. The aircraft arrived over the target in clear visibility at 9,855 metres (32,330 ft). During the journey, Navy Captain William Parsons had armed the bomb, which had been left unarmed to minimize the risks during takeoff.

His assistant, 2nd Lt. Morris Jeppson, removed the safety devices 30 minutes before reaching the target area.

About an hour before the bombing, Japanese early warning radar detected the approach of some American aircraft headed for the southern part of Japan.

An alert was given and radio broadcasting stopped in many cities, among them Hiroshima. At nearly 08:00, the radar operator in Hiroshima determined that the number of planes coming in was very small?probably not more than three?and the air raid alert was lifted. To conserve fuel and aircraft, the Japanese had decided not to intercept small formations. The normal radio broadcast warning was given to the people that it might be advisable to go to air-raid shelters if B-29s were actually sighted, but no raid was expected beyond some sort of reconnaissance.

The release at 08:15 (Hiroshima time) went as planned, and the gravity bomb known as “Little Boy”, a gun-type fission weapon with 60 kilograms (130 lb) of uranium-235, took 57 seconds to fall from the aircraft to the predetermined detonation height about 600 metres (2,000 ft) above the city. Due to crosswind, it missed the aiming point, the Aioi Bridge, by almost 800 feet (240 m) and detonated directly over Shima Surgical Clinic.

It created a blast equivalent to about 13 kilotons of TNT. (The U-235 weapon was considered very inefficient, with only 1.38% of its material fissioning.) The radius of total destruction was about one mile (1.6 km), with resulting fires across 4.4 square miles. Americans estimated that 4.7 square miles of the city were destroyed. Japanese officials determined that 69% of Hiroshima’s buildings were destroyed and another 6?7% damaged.

70,000?80,000 people, or some 30%of the population of Hiroshima were killed immediately, and another 70,000 injured. Over 90% of the doctors and 93% of the nurses in Hiroshima were killed or injured; most had been in the downtown area which had been greatly damaged.

The energy released by the bomb was powerful enough to burn through clothing. The dark portions of the garments this victim wore at the time of the blast were emblazoned on to the flesh as scars, while skin underneath the lighter parts (which absorb less energy) was not damaged as badly.

Although the United States had previously dropped leaflets warning civilians of air raids on twelve other Japanese cities, the residents of Hiroshima were given no notice of the atomic bomb.

Japanese realization of the bombing

The Tokyo control operator of the Japanese Broadcasting Corporation noticed that the Hiroshima station had gone off the air. He tried to re-establish his program by using another telephone line, but it too had failed.

About twenty minutes later the Tokyo railroad telegraph center realized that the main line telegraph had stopped working just north of Hiroshima. From some small railway stops within 16 kilometers (10 mi) of the city came unofficial and confused reports of a terrible explosion in Hiroshima. All these reports were transmitted to the headquarters of the Imperial Japanese Army General Staff.

Military bases repeatedly tried to call the Army Control Station in Hiroshima. The complete silence from that city puzzled the men at headquarters; they knew that no large enemy raid had occurred and that no sizeable store of explosives was in Hiroshima at that time.

A young officer of the Japanese General Staff was instructed to fly immediately to Hiroshima, to land, survey the damage, and return to Tokyo with reliable information for the staff. It was generally felt at headquarters that nothing serious had taken place and that the explosion was just a rumor.

The staff officer went to the airport and took off for the southwest. After flying for about three hours, while still nearly one hundred miles (160 km) from Hiroshima, he and his pilot saw a great cloud of smoke from the bomb.

In the bright afternoon, the remains of Hiroshima were burning. Their plane soon reached the city, around which they circled in disbelief. A great scar on the land still burning and covered by a heavy cloud of smoke was all that was left. They landed south of the city, and the staff officer, after reporting to Tokyo, immediately began to organize relief measures.

By August 8, 1945, newspapers in the US were reporting that broadcasts from Radio Tokyo had described the destruction observed in Hiroshima. “Practically all living things, human and animal, were literally seared to death,” Japanese radio announcers said in a broadcast captured by Allied sources