After the nuclear crisis in Japan in 2011, the US government decided to start the development of a new weapon that was supposed to have the explosive power of an atomic bomb, but has significantly smaller side effects and radiation. The project, which was classified as top secret, was startet in early 2012 and got the codename "Project 401".
But because the scientists weren't able to reach the explosive power of a nuke with conventional methods, the scientists picked up the principle of the atomic bomb, but believed they could reduce the amount of emitted radiation by adding some special substances. Five years later, in summer 2017, the development team believed they made a first breakthrough and manufactured two prototypes. In the conviction that the bomb will release only a very small amount of radiation, the government approved a top secret weapon test in Nevada in fall 2017. On October, the 14th 2017, the first prototype was fired in the desert. But the results were catastrophic: The explosion power was as big as a nuke, but the emitted radiaton was also many times over the amount of a normal atomic bomb. Many operators and scientists got sick in the following months and suffered from acute radiation syndrome. After the incident became public, many human rights and environmental protection organisations protested; the US stood shortly before loosing their face. To keep their international esteem, the US admitted the existence of the project, but called the weapon test an accident and claimed that there is no other prototype. The project was stopped officially.
But in 2018, a whistle blower published information about the second prototype. The government decided to send the second prototype abroad and modified an ohio-class nuclear submarine to carry the bomb. On April the 18th 2018, the submarine put to sea. But two days later, the submarine vanished from the radar. There is no information about that incident. The investigations were stopped at the end of 2019.
In the middle of 2020, the NASA noticed slightly increased radiation above some small islands in North Korea. After some investigations several hints came up, showing that North Korea could be responsible for the missing submarine.
Because the political climate between North Korea and the USA got worse, the USA feared an attack with the P401-prototype. This would not only cause the death of millions of people, but also the end of the USA as we know it and unpredictable consequences for the whole western civilisation. Due to that, the US army decided to send a small special forces team, equipped with experimental nano gear, to North Korea to look for the missing bomb and seize it as fast as possible.
