To achieve the modernization of the UK's nuclear forces,Margaret Thatcher had to make a choice after she had became the Prime Minister whether continue to improve the existing nuclear missile system or purchase a new generation system from the US. Finally,Thatcher chose to conclude the "Trident" missile agreements with the US in order to consolidate the military-political alliance between the UK and US. These agreements were more conducive to the UK than previous ones,and the US also achieved its own goals,which has helped to raise both the Anglo-American nuclear alliance relationship and the "special relationship" between the UK and US to a new historical height.