In 2010 U.S. President Barack Obama stated that nuclear terrorism was “the single biggest threat to U.S. security, both short-term, medium-term and long-term”. The events of September 11, 2001 demonstrated the real risk of catastrophic terrorism. It also exacerbated existing fears that groups such as Al-Qaeda would be willing to detonate a nuclear device either on U.S. territory or American valuables abroad. It is one thing to hijack a plane and crash it into a building. It is quite another challenge to obtain a nuclear weapon or the materials needed to assemble a nuclear bomb. Unlike ‘conventional’ arms which proliferate much more easily in the international system, nuclear weapons are much harder to assemble or obtain; a terrorist group would need a state’s assistance to do this. This has raised the issue of terrorism as a technique – that a state might resort to nuclear attack by proxy against the United States and its allies in order to avoid attribution.