Area 51 series by Bob Mayer (alias: Robert Doherty)

In the late 1940s, two flying saucers (called "bouncers") and a mile long spacecraft with an interstellar drive were discovered in the remote Nevada desert, with information that leads to the locations of seven more abandoned flying saucers hidden beneath the frozen tundra of Antarctica, which the US takes back in Operation Highjump. As the massive "mothership" is too large to relocate and so little is known about its alien technology, a secret military base is built around the area surrounding the mothership, known as Area 51. It is here that the United States government spends the next sixty years trying to unravel the secrets of the alien technology.