[Llarry]

Slight threadjack here, but the original radar sites were really meant to detect Soviet bombers, not missiles. By 1957 -- thanks to the U-2 photo overflights of the USSR -- we realized that the Soviets did not have a huge bomber force as we had feared. But then with Sputnik came the ballistic missile threat, so the defensive effort continued.

The U.S. Navy contributed a seaward extension of the defensive radar effort in several forms:
-- Lockheed WV-2 Warning Star radar-equipped early warning aircraft. Based on the C-121 Constellation, over 140 WV-2 (later EC-121) aircraft were bought by the Navy to extend the "radar horizon" to sea. These initially flew from bases in Maryland and Hawaii, but then the main effort in the Atlantic was relocated to Argentia, Newfoundland and later would also fly to Keflavik, Iceland. The Hawaii-based WV-2s would refuel at Midway Island during their long missions.
-- Goodyear ZPG-2W and -3W radar equipped blimps were used on the Atlantic side, flying from Lakehurst, New Jersey. The Navy retired all the blimps in 1962.
-- Radar-equipped DERs (Destroyer Escort with radar mods) keeping station about 300 miles off both U.S. coasts. By 1957, there were 36 of these ships; they were leftover World War II ships that were converted with extensive electronics, including both long-range air search and height-finding radars.
-- By the late 1950s the DERs were supplemented by larger AGRs (radar picket auxiliary ships), converted from leftover cargo ships from WWII; 16 of these were active, evenly split between Atlantic and Pacific. The AGRs were even more elaborately equipped with electronics.

By the 1960s, the converted ships were showing their age and began to be retired and then the Vietnam war preoccupied the Americans and the barrier patrols just sort of petered out. The personnel who manned the ships and planes were dubious about the value of their efforts, which also involved patrols in the upper latitudes of the seas, with rough seas and generally poor weather conditions.