How did the US respond to bombings on Darwin?

Answer 1

first answer:

After the Bombing of Darwin the US responded by protecting Darwin and Papua New Guinea. This wasn't necessarily for the Australians' sake but for an American advantage in the war.

second answer:

The Japanese attacks on Australia, including the attacks against Darwin starting on 19 February 1942, pushed the Australian government to demand of the British leadership that Australian air & land units currently fighting against the Germans & Italians in Egypt & Libya be withdrawn for the immediate defense of Australia. These Australian units were essential for the British defense of Egypt and the Australian demand created a crisis for British leadership.

The crisis was resolved when the British requested that the United States officially assume responsibility for the defense of Australia, and the United States accepted. The Japanese threatened all British territories in the Pacific & Asia (including most especially India). It was also clear to the British & Australians that the defeat of Japan would primarily be the responsibility of the United States for many reasons, and it made sense to provide whatever bases were needed in this effort. Australian units stayed in the Middle East. American air, naval & land units reinforced the newly mobilized Australian units in Australia & New Guinea. Additionally the United States shipped large amounts of supplies & equipment to Australia for both military & civilian use to supplement the British supplies. The United States also helped to expand & modernize ports & airfields throughout all of the region to facilitate Australia becoming a significant staging area for the coming offensive in the South Pacific against Japan. Australian & New Zealand military units worked in concert with the United States military in this area to first stop, then push back the Japanese. It was the Australian combat troops in New Guinea that were the first to stop a Japanese offensive and disprove Japanese invincibility in Jungle combat. Australian & native coast-watchers were also essential during the first two years in the war.

This arrangement was beneficial to all the Allied Powers, especially the United States that needed the Australian & New Zealand bases to help defeat Japan

Answer 2

The population of northern Australia was evacuated, and a defensive line was set up based on the 'Brisbane Line'. This was an over-reaction as the Japanese had no intention (or capability) of invading Australia. However Western Australia, which was virtually undefended, told the Federal Government to either defend it or they would have to come to terms with the Japanese. Three divisions were deployed to Western Australia.