''On this anniversary may the United States and Australia recommit as allies, partners and friends,'' President Obama said in a statement read by US ambassador John Berry at the Australian-American Memorial at Russell Offices on Thursday.

Mr Obama said while the alliance was not formalised until the signing of the ANZUS treaty in 1951, it had come into being on the battlefields of the Pacific between 1942 and 1945.

''During those fateful days on the Pacific our countries fortified an unshakeable alliance based on shared histories and rooted in common values,'' he said. ''It has blossomed over the decades to become one of the cornerstones of peace and security, not just in the Asia-Pacific region but around the world.''

Mr Abbott, who paid tribute to the hundreds of American sailors and airmen who lost their lives during the battle credited with having ''saved'' Australia, said in a statement the Pacific war had hung in the balance for five days.

''It was then that our strategic alliance [later formalised as ANZUS] was forged,'' he said. ''The front line of World War II had advanced towards the Australian coastline and only the garrison at Port Moresby stood in the way.''

The four-day battle, which cost the Japanese five ships and 966 men and the Allies three ships and 656 men, halted the Japanese seaborne assault on Port Moresby and weakened the Japanese fleet before the Battle of Midway a month later.

General Sir Peter Cosgrove, attending the ceremony for the first time as governor-general, said the Battle of the Coral Sea marked the first major Japanese defeat of the war and the first defeat the Japanese navy had ever suffered.

He said that when the Japanese bombed Pearl Harbour and Darwin in late 1941, large numbers of Australian troops had already been sent abroad to fight in the Middle East.

''Not enough men were left to defend our home,'' he said. ''It was then that Curtin [the Australian prime minister] appealed to the US and the US came through for us.''

While the battle is now regarded as a major victory and a turning point in the war, a ''friendly fire'' incident and Australian disappointment at the number of Japanese vessels sunk caused serious friction, and terse words, between Australian commanders and their US counterparts at the time.

Rear Admiral John Crace, the Canberra-born commander of Task Group 17.3 comprising HMAS Australia, HMAS Hobart, USS Chicago, USS Farragut, USS Perkins and USS Walker, reported being attacked by two waves of Japanese torpedo bombers in the space of 10 minutes on the afternoon of May 7, 1942.

Minutes after the last Japanese plane left, Task Group 17.3 was attacked by three American B-26 Marauders from Townsville.

''Fortunately their bombing, in comparison to that of the Japanese formation minutes earlier, was disgraceful,'' Rear Admiral Crace wrote in his report.

While the Americans, including General Douglas MacArthur, denied the mistake, they did agree to give pilots additional training on the identification of shipping.

On May 13, the Australian chiefs of staff regretted that more Japanese ships had not been sunk and asserted too few land aircraft were based in north-eastern Australia.

MacArthur, in a written response to Curtin, said he was disappointed and that he regarded the battle as ''a very brilliant effort which undoubtedly saved Australia from a definite and immediate threat''.

The following day he announced plans to establish aerial bases on the south-east coast of Papua.