Japan's Emperor Akihito has arrived on the island of Saipan to pay respects at a memorial to the country's war dead.
About 2.4 million Japanese troops died during World War II
The trip is the first the emperor has made to a WWII battlefield abroad, although he has spoken of Japan's regrets over its wartime past.
Some 43,000 Japanese soldiers, 12,000 civilians and 3,500 US troops died during almost a month of fighting on the then-Japanese island in mid 1944.
The visit comes amid tensions with China and South Korea over the war.
The battle for Saipan, often described as the Pacific D-Day, was a key victory for the US.
Capture of Saipan allowed US generals to base B-29 bombers on the island, from where they bombed Japan's mainland cities.
The atomic bombs dropped on Hiroshima and Nagasaki in 1945 were launched from aeroplanes that took off from the neighbouring island of Tinian.
During his trip, Emperor Akihito will visit an official Japanese monument on the island, which is now a US territory.
He will start his visit at two notorious cliffs - Banzai Cliff and Suicide Cliff - where hundreds of people threw themselves to their death when defeat appeared certain.
"Sixty-one years ago today, a fierce battle was still being fought on this island," the emperor said before leaving Tokyo with Empress Michiko.
Emperor Hirohito's war legacy is a key issue for Emperor Akihito (r)
"Our hearts ache when we think of those people who fought at a place where there was no food, no water, and no medical treatment for the wounded."
Saipan veteran Seiichi Oike, 87, was among just 2,000 Japanese to survive the battle.
"Those who fought then were soldiers of the emperor, and they and we who remain are happy that he is coming to comfort their souls," Mr Oike told Reuters.
Emperor Akihito has visited South Korea and China in the past, where he has expressed remorse for Japan's wartime actions, but he has steered clear of an explicit apology.
Many observers feel his visit to Saipan is designed to win headlines within Japan, at a time when relations with China and South Korea have deteriorated rapidly.
Both countries are angry at what they see as Japan's reluctance to come to terms with its imperial aggression.
Japanese Prime Minister Junichiro Koizumi recently visited the island of Okinawa.
Earlier in June he paid respects at a memorial at Iwo Jima, site of another key battle.