In the Queensland city of Townsville, Prime Minister Malcolm Turnbull has led the first of many commemorations to thank Australian and American servicemen who fought in the Battle of the Coral Sea.
"Over four critical days in May 1942, the fate of our island continent hung in the balance. It was a turning point in the war," he told the dawn service.
"Our freedoms were secured by the bravery of the fighting men on those ships and the pilots who flew through everything the enemy and the weather could throw in their way."
PM honours Coral Sea service men and women
The Japanese had struck the US naval base at Pearl Harbour, taken the British garrison of Singapore and had bombed Darwin.
As the Prime Minister recalled, their next aim was to seize Port Moresby and isolate Australia.
"The Japanese were turned back, but not without a heavy price. The mighty aircraft character Lexington was lost, as was the destroyer USS Sims and tanker USS Neosho," he said.
"The US Navy's commitment of two of the carriers into the battle showed a total commitment to the defence of Australia. And it showed a total unity of purpose."
Cecil Wiswell was a 17-year-old seaman on the USS Lexicon when it was torpedoed by the Japanese.
Coral Sea Battle Veteran Cecil Wiswell Source: ABC - Andrew Greene
The now 93-year-old is in Australia for the commemorations and spoke to the ABC about his survival.
"It brings back memories when I look out there on the sea. I stayed aboard the ship. I helped the doctor with patients for a while and then I went around the ship trying to fight fire and what-not," he said.
"We stayed a board for quite a while after 'abandon ship' was sounded and all of a sudden, it dropped what felt like two or three feet more, I said It's time to leave now. I went to a life raft but the life raft had so many men in it and around it that it was submerged. I said 'this is no place for me' so I let out alone."
The ashes of his fellow Lexington crew member, Harry Fry, have been scattered in the Coral Sea.
The Prime Minister will later this week attend a commemorative dinner in New York, where he will have his first face-to-face meeting with US president Donald Trump.
"We must be forever grateful to those who put their lives on the line and those who do so today so that we might have a free and peaceful world," Mr Turnbull said.
