Context
This project was initiated just after the close of the Korean war, in 1953, during which UN forces, primarily led by the United States, supported the South Korean government, fought the North Korean government, supported by Chinese Forces and material aid from the Soviet Union. In this bitter conflict, US General Macarthur requested (and was denied) use of tactical nuclear weapons to attack Manchuria, with the goal being to halt the flow of PRC troops into the battlezone. General Curtis Lemay, then head of Strategic Air Command, largely presided over an area bombing campaign that destroyed much of North Korea. Even after the outcry over so called "area Bombing" or indiscriminate targeting of civilians during world war II, the policies of total warfare and targeting of civilian population centers continued with a vengeance. Many believed that the future of warfare would be largely fought from the air, and that it would be devastating in unprecedented ways, largely thanks to the development and proliferation of nuclear weapons.
In Russia and the United States, more an more nuclear bombs were being produced. Conventional armed forces were being expanded as well. The two nations had opposing economic systems, propaganda that vilified the opposing side, and multiple atrocities under their belt that the opposing side could point to as indication of their moral failings. All this came together to create the high-stakes diplomatic game of nuclear deterrence.
The basic idea of deterrence is that enemies will not want to harm you if you can respond overwhelmingly, or at least with enough force to make the enemy consider an attack too costly. Nuclear deterrence is the ultimate expression of this concept. With multiple grievances, and little common ground to stand on, governments such as the US and the Soviet Union judged that the only way to be absolutely sure that their adversaries will not devastate them with nuclear weapons is to prove that they could strike back, and devastate the attacker.
It is in this grim milieu that Project Pluto was born. In 1954 when the project was proposed, nuclear Intercontinental Ballistic Missiles had not yet become the proven workhorse they are today. Bombers were the primary method of getting nuclear weapons to their targets. However, bombers can be shot down, tracked on radar, and assaulted by other air assets.
The Air Force that the Atomic Energy Commission felt they needed a way to carry atomic bombs to a target quickly, without risk of interception. Nuclear propulsion seemed like it could provide the answer. This wasn't a weapon designed to be used for regular, conventional warfare. This was a weapon of deterrence. Of fear. It was purpose built for the end of the world.