For a seat and a breather you must go to another part of the museum, the east wing, which most visitors pass through quickly, with a brief glance at the uninspiring exhibits on the wall. There are wordy panels of text, in Japanese and English, a few black and white photographs, and some glass cases containing mouldy uniforms and rusty guns. Nothing to compete with the horrors upstairs. But this, ironically, is the most controversial corner of the whole museum. Its contents cast the whole story in a very different light.
The east wing opened just two months ago, after years of lobbying, resistance and compromise among the many competing pressure groups and local government departments that form the collective conscience of Hiroshima. Very simply (and, it must be said, boringly) it tells the other side of the story of death and suffering movingly documented in the main exhibit. If Hiroshima is famous today as a self-styled city of peace, it was for most of its modern history the centre of one of the most important military-industrial complexes in Japan. In discreet ways, it still is.
Hiroshima's military importance arose naturally from its geography. At the head of a wide bay in the western end of the still Inland Sea, the city is built on a flat delta of six rivers, protected from the north by a horseshoe of mountains. Its sheltered position was the most chilling of the several factors which made it an ideal laboratory for the atomic bomb: isolated from storms and prevailing winds, the effects of the atomic fall-out could be measured with precision.
In medieval Japan, pirates had made a tidy living raising "taxes" from the local fishing villages, but it wasn't until the 19th century that the city came into its own. In 1868, after 350 years of self-imposed isolation, the ruling shoguns were deposed by a samurai clique in the name of the Emperor Meiji. Japan opened its ports to the outside world and began to modernise - and arm - rapidly.
As the major castle town of western Honshu, the main island of Japan, Hiroshima took a leading role. In 1877 troops from the city put down an uprising in the south-west. Five years later they were sent to Korea, later to become an imperial colony, to "protect" the Japanese consul in Seoul. In 1888 the Imperial Naval Academy was relocated to Etajima island, a 20-minute boat ride from Hiroshima harbour. In the 1890s, Japan's surprise victory in the Sino-Japanese War was planned, supplied and directed from Hiroshima. The Emperor Meiji spent most of the war in the castle which was briefly the de facto capital of the country.
The campaigns waged by the city's Fifth Army Division are a precis of the successes and swelling ambitions of the Imperial Forces in Asia, up to and throughout the Second World War: the Boxer Rebellion in 1900, the Russo-Japanese War in 1904-5, the Liaotung Peninsula in 1914, Korea and Siberia in 1919. Throughout the autumn and winter of 1931, army divisions sailed from Hiroshima to invade Manchuria: the Fifth Division was there for the Rape of Nanking in 1937, when as many as 300,000 Chinese soldiers and civilians were massacred by Imperial troops, one of the most controversial episodes of the war and the subject of hot debate among Japanese historians. The panel in the Peace Museum dealing with the massacre has a piece of paper glued over the original text, on which a less contentious version ("Several views exist regarding the number killed") has been substituted.
The area became a centre of shipbuilding and armaments manufacture in factories run by Mitsubishi Heavy Industries: the battleship Yamato, the biggest ever made, was launched from the neighbouring city of Kure. During the same period, the isolated islands of the Inland Sea were turned to sinister military uses: Ninoshima became a quarantine station for troops infected in Manchuria; on Okunojima, a secret factory produced thousands of tons of poison gas. There was a constant traffic of military supplies, ordnance and personnel. Within a mile of the A-bomb's ground zero were incinerated the Infantry First Reserve, the Field Artillery Reserve, the Transport Reserve, the Hiroshima First and Second Army Hospitals and, in the 400-year-old castle, the military HQ of western Japan.
One of the most fascinating things about the modern city of peace is how intact many of its military traditions remain. Hiroshima is as strategically important as it has always been, and a discreet but enormous post-war military presence has remained in place since the first US troops landed in August 1945. At nearby Iwakuni is the biggest US Marine base in the country after Okinawa. Supersonic jets regularly scream over the Inland Sea, and Mitsubishi Heavy Industries' factories and plants in Hiroshima prefecture are the biggest suppliers of arms and explosives in the country, at the high-tech edge of military research. In May there was a scandal when it was revealed that the apocalyptic cult Aum Shin Rikyo, suspected of the Tokyo subway nerve gas attack in March, had broken into a Mitsubishi facility and stolen information relating to laser weapons. Japan's constitution has so far prevented its participation in active UN oper- ations but, when it does, the area will again play its part. In 1991 Japanese mine sweepers from Kure took part in mopping-up operations after the Gulf War.
On Etajima, the Imperial Navy has been supplanted by its successor, the euphemistically named Maritime Self-Defence Forces, but the Naval Academy is still there, along with a museum recording the achievements of its predecessor. It's not found in any of the many English-language guides to the city. "Hiroshima people don't talk much about Etajima," according to Minoru Omuta, president of the Hiroshima Peace Culture Foundation. "They don't even know that there's a military training school there and a museum." The Hiroshima Citizens Group Against Nuclear Power Plants recently published a book with the rhetorical title, Is Hiroshima A City Of Peace? Its members have received threatening letters and phone calls from right- wingers and supporters of an expanded military.
"The new museum is a start, but most Hiroshimans don't know about the military situation, or maybe they don't care," says group organiser Shoji Kihara. "People insist on talking only about the bomb, but they're blind to what is around them."