The Ethan Allen SSBN class, were the first US Navy submarines really designed from the outset to launch ballistic missiles. They were constructed using submarine design SCB-180 and were built with Hy 80 high-strength steel, which allowed them to reach greater depth than any previous submarine. Five submarines comprised this class that entered service between 1961-62, making their first deterrent patrols at the end of 1962. They were armed with sixteen Polaris A-2 missiles, being replaced by the Polaris A-3 in 1965, which would be replaced in mid of the 70’s by the Polaris A-3T. In 1983 these submarines withdrew from service, except 2 units, which were converted into nuclear attack submarines (SSN) especially fitted to carry out Special Operations missions with the US Navy SEALs until 1992, when they were definitively withdrawn.