Three days after an atomic bomb devastated Hiroshima, six-year-old Kazuko Uragashira and her parents were aboard an evacuation train out of their charred home city.

Today marks the 65th anniversary of the Hiroshima bombing.

Having narrowly survived the nuclear inferno, the family headed for the home of an uncle, not knowing that another date with destiny lay ahead of them. His home town was Nagasaki.

Ms Uragashira remembers sitting on the train, her legs burnt from the radioactive blast, when their train stopped in a tunnel outside Nagasaki after a 300-kilometre journey.

“It was another scene from hell,” Ms Uragashira, now 71, recalled. They had stumbled into the immediate aftermath of the second atomic bombing in Japan, on August 9, 1945.

As the train passengers painstakingly trudged their way through the carnage, she saw survivors with molten skin dripping off their bodies.

“I still remember the smell of charred bodies and the weak screams of the dying, for water... Even if I suffer dementia, I will never forget it,” she said.

Ms Uragashira, who now lives on a remote island off Nagasaki, is one of the few remaining “niju hibakusha” – survivors of not one but both US atom bomb attacks on Japan in the final days of World War II.

“I was lucky as a lot of others died instantly, but I still want to know why such a horrible thing happened to me twice,” she said quietly.

An estimated 140,000 people died instantly in Hiroshima or succumbed to burns and radiation sickness soon after the blast, and over 70,000 perished as a result of the Nagasaki attack three days later.

Today’s ceremony will also commemorate the thousands who survived the blasts but spent their lives living with its after-effects, with many suffering leukaemia and other cancers.

Around 150 people, like Ms Uragashira, are thought to have been exposed to both bombings.

The only person officially recognised as a survivor of both bombs, Tsutomu Yamaguchi, who died in January aged 93, once told an interviewer: “I thought the mushroom cloud had followed me.”

Film director Hidetaka Inazuka has recorded testimonies by double bomb survivors to keep alive their memories.

Milestones in post-World War II Japan-US relationship

After its World War II surrender following the atomic bomb attacks on Hiroshima and Nagasaki, Japan was occupied by the US and then became its strongest ally in Asia.

In recent months, the Cold War-era alliance has suffered after a new centre-left government in Japan said last year it may move a contentious US airbase off Okinawa island, before reversing the plan.

Here is a chronology of major events in the relationship.

1941

• December 7: Japan attacks Pearl Harbour naval base, Hawaii.

• December 8: US Congress declares war on Japan.

1945

• March: US forces invade Japan’s Okinawa island.

• August 6: US drops atomic bomb on Hiroshima.

• August 9: US drops atomic bomb on Nagasaki.

• August 15: Japanese Emperor Hirohito surrenders.

1947

• Japan’s war-renouncing con­stitution, drafted by occupation force the US, comes into effect.

1951

• Japan-US security treaty signed.

1954

• Japan Self Defence Forces established.

1956

• Japan admitted to the United Nations.

1960

• New Japan-US security treaty and related agreements signed.

1960s-1980s

• Japanese economy grows rapidly.

1972

• US returns Okinawa island to Japan.

1974

• Gerald Ford becomes first sitting US President to visit Japan.

1975

• Emperor Hirohito visits the United States for the first time.

1980s

• Japan-US trade disputes heighten, particularly over cars.

1989

• War-time Emperor Hirohito dies.

1995

• US servicemen gang-rape a 12-year-old girl in Okinawa, fuelling anti-US military sentiment in Japan.

1990s-2000s

• Japan falls into two decades of economic stagnation.

2004

• Japan sends non-combat troops to Iraq to support US-led war, their first post-World War II overseas deployment to an active war zone.

2006

• Japan and the US agree on the realignment of US bases on Okinawa.

2009

• Japan-US relations rocked after Japan’s then Prime Minister Yukio Hatoyama pledges to review the 2006 deal and move a US airbase outside Okinawa.

June 2010

• Hatoyam, after months of US pressure and amid sagging domestic support for his bungled handling of the issue, vows to stick with the original US base deal. He resigns and is replaced by Prime Minister Naoto Kan.