In 1957 the US did not have an operational ICBM so Thor IRBM bases needed to be located in a European NATO country.
The simple 'formula' to explain this is.........
A number of locations was considered..........UK, Italy, France (together with Turkey, Alaska and Okinawa).
France had already refused to accept Jupiter missles so there was little prospect of that country accepting Thor.
The Italians were also very reluctant but finally accepted in principle a willingness to accept two Thor bases.
As time dragged on, voices in the US were questioning the need for IRBMs in Europe as the US based ICBM programme was progressing well.
US Secretary of State for Defence, Neil McElroy stated, "The farther we go down the road towards an operational capability of the ICBM, the less interesting it is for us to deploy IRBMs".
In March 1957 it was reported that, in Bermuda, "The President of the United States and the Prime Minister of Great Britain exchanged views during the past three days on many subjects of mutual concern."
President Eisenhower and Harold Macmillan at the Bermuda Conference in March 1957
Despite some misgiving within both countries, this conference ultimately led to the establishment of Thor missiles bases in the UK.
On the 30th January 1958, President Eisenhower and the National Security Council formally agreed on the establishment of Thor missile squadrons in the UK and the full agreement between the US & the UK was signed in February 1958.
The main points in the agreement were: