By February 1946, the USA had been pushed back everywhere. In the Pacific, Australia and New Zealand had been taken by Japan, along with Hawaii and the Aleutians. America was pinned behind the Pacific and Atlantic Oceans. However, an invasion of the US was considered impossible by both the Germans and the Japanese. Somehow, a knockout blow had to be made to defeat the Americans and end the war. In March of 1944, the Germans tested a new weapon, developed by Professor Kurt Diebner. This weapon was the first atom bomb ever to be tested. However, Hitler wanted a more powerful bomb, and thus work on making Diebner Atom bombs was stopped after only two were made.
In January 1946 a new fast fission Atom bomb was tested in Russia. The yield was 40KT. Here at last was a weapon to end the war with.
The plan made by the German High Command was to hit New York with a Nuclear Weapon. Rockets were planned to be used. Building a suitable rocket took some time, until eventually a A10/11 two stage rocket was completed for use. The other cities were to be hit by Diebner Bombs, which though weaker, would still do heavy damage. On the early morning of the 4th of March, the first of the rockets took off. The A10-11 was first, 1.4 Million Kg of thrust pushing the rocket into space.
The World entered the Nuclear age at 10:07 AM on March the Fourth, 1946. Five sq mi of New York was destroyed instantly and the initial death toll was estimated at 120,000, with tens of thousands more dying in the following 48 hours. The rest of the city was in ruins. The Empire State Building ceased to exist and firefighters struggled to control the inferno raging on the mainland. At the same time two smaller 1KT atom bombs hit Philadelphia and Boston, doing far less damage but still ruining the cities. Franklin D. Roosevelt was visiting New York, and was killed by the blast. This led to a massive political crisis, and the voices of the isolationists were heard stronger than ever. America signed an Armistice on April 20th, 1946, The Treaty of Tokyo.
The destruction of New York, Boston and Philadelphia finally convinced the US that the war was unwinnable, and on the Führer's Birthday, 20 April 1946, the Second World War came to an end.