Short answers, pulled from the story.
The Polaris missile program began in the summer of 1956 when a study group gathered at Nobska Point for Project NOBSKA. Edward Teller promised that a one-megaton warhead could be built within five years to shift naval missile development away from liquid-fuel Jupiter rockets.
The first operational version designated Polaris A-1 entered service in late 1961 with a range of nine hundred nautical miles. It carried a single W-47-Y1 nuclear warhead weighing six hundred kilotons and had an inertial guidance system providing a circular error probable of three thousand feet.
Thirteen submarines received the A-2 model which served until June 1974. Ongoing problems with mechanical arming equipment led to large numbers of missiles being recalled for modifications before retirement.
Britain received Polaris missiles and fire-control systems from the United States under the Nassau Agreement signed on the 6th of April 1963. Harold Macmillan met John F. Kennedy to finalize terms while Italy received Jupiter missile upgrades during reconstruction programs between 1957 and 1961.
The Chevaline program added multiple decoys chaff and defensive countermeasures to penetrate Soviet anti-ballistic missile screens. The system became operational on HMS Repulse in mid-1982 and equipped all British SSBNs by mid-1987 before being withdrawn from service in 1996.