Australia was a key to Japanese war plans in the Pacific, because it was a base for land, air and sea operations against them. In turn a key to controlling Australia was New Guinea. 

If Japan could control Port Moresby in New Guinea, then it could constantly attack Australia's land, sea and air forces. So, whoever controlled New Guinea, controlled Australia as a supply base. 

From the Japanese entry in the war in December 1941, they had been an unstoppable military power in the Pacific. In May they were ready to land an invasion force by sea to capture Port Moresby. They had two fleets ready - the invasion fleet, and a naval fleet to protect the soldiers, and to fight the American warships in the area.

Between 5 and 8 May 1942 the Battle of the Coral Sea was fought. The fighting was done by aircraft against ships. Allied land- and carrier-based aircraft flew against the Japanese ships, and the Japanese carrier-based planes tried to destroy the American fleet.

Right: A cartoon which appeared in the Sunday Telegraph on May 10, 1942. Written on the side of the sunken ship is "HON. JAP INVASION PLANS".

A tally of Japanese losses in the Battle of Coral Sea showed light carrier Shoho, destroyer Kikuzuki, and three small naval units sunk, carrier Shokaku damaged, some 77 planes lost, and a total of 1,074 men killed or wounded.

On the other hand, losses inflicted on US forces, as learned after the war, were carrier Lexington, oiler Neosho and destroyer Sims sunk, carrier Yorktown damaged, 66 planes lost, and 543 killed or wounded.

After the battle, the Japanese ordered their invasion fleet to withdraw. The attack on Port Moresby would have to be by the troops going overland from the Buna area, across the Owen Stanley Mountain range, to Port Moresby. The mountainous terrain was very difficult for the troops, and Japanese supplies were not able to get to the men as they moved forward. Eventually, the Japanese were defeated on the Kokoda Track by Australian troops, and Port Moresby was safe. 

The above based on:

• 'Battle of the Coral Sea' by Peter Dennis (ed), The Oxford Companion to Australian Military History, Oxford University Press, Melbourne, 1995; and

• Mitsuo Fuchido and Masataku Okumiya, Midway. The Battle that Doomed Japan, Hutchinson, 1957, pp 115 - 116