The US Naval Security Group (NAVSECGRU) was an organization withing the US Navy tasked with intelligence gathering. A large part of this was signals intelligence (SIGINT) gathering, cryptology, and information assurance. NAVSECGRU was active from 1935 to 2005 when it was folded into the Naval Network Warfare Command (NETWARCOM).
SIGINT is intelligence gathering by interception of signals between people (communications intelligence, aka COMINT) or electronic signals not used for direct communications (electronic intelligence, aka ELINT). Sensitive information is generally encrypted and this is where cryptologists would enter the equation.
Often times, the US would fly planes near sensitive Soviet Bloc countries to arouse suspicion and cause the Soviets to use their radar and communications systems. The ELINT specialists would then soak up as much information as they could, interpret it, and send it off to the appropriate parties within the military to give us a better understanding of the Soviets' capabilities.
Corea served the US Navy not only as an important site for SIGINT but also as a training ground for the entire Classic Wizard System globally, for maintenance, tuning, support, and operation, with the last class graduating in 2001. The Classic Wizard System was a high frequency direction finding (HF/DF) network which the Navy used to track and target enemy ships. Sites like Corea would use their Wullenwebber Antenna Array in conjunction with ELINT satellites to triangulate the location of foreign warships. Not only did this enable the US Navy to track these vessels, but it also provided cruise missile-equipped vessels ships with over the horizon targeting capabilities. The nearby Winter Harbor facility served as the main base and provided housing, recreation facilities, a chapel, mess hall, and the other necessities. The US Navy operated here from 1935 until 2002, when it was excessed by the Department of Defense.
The Winter Harbor facility was a replacement for an existing radio site across Frenchman Bay on Otter Cliffs (south of Bar Harbor). The Naval Radio Station at Otter Cliffs was built in 1917 and was the Navy's best transatlantic radio site because it had an unobstructed shot across the ocean and because Mount Desert Island was so isolated that there was no other radio noise. By the 1930's, the site's buildings were run down and needed replacement badly.
John D Rockefeller suggested that the site be removed and that the Navy included it with his land donation to Acadia National Park. The Navy agreed, provided that Rockefeller built a replacement site. Rockefeller had a site constructed across the bay on the Schoodic Peninsula, which was commissioned in 1935 and grew into the US Navy's Winter Harbor facility.
Typical life span for the satellites used was 7-8 years. With the last batch of satellites being launched in 1995, closing the site in 2001 and excessing it in 2002, timed out about right.
The site's Wullenwebber Antenna was probably the feature by which it was most commonly identified. Often called an elephant cage because of its ring shape and tall antenna poles, the Wullenwebber was a Circulalary Disposed Dipole Array (CDDA) that used vertical radiator elements in a ring with vertical reflector elements installed behind them in a smaller diameter ring for high frequency direction finding.