The radar is installed on Estonia's Muhu Island but can be rapidly deployed elsewhere if needed.
"The entry into service of the Ground Master 400 is an important milestone in our air defense program," said Ingvar Parnamae, Undersecretary for Defense Investments of the Estonian Ministry of Defense. "We look forward to the operational benefits of this new radar."
The two GM 400s ordered by Estonia are part of a 14 system order by Estonia and Finland and will be connected to NATO's air defense network, thus being interconnected with all the other European air defense radars.
The Ground Master 400 provides enhanced detection of threats at low and high altitudes and is also is easier to maintain.
"We are delighted that the GM400 radar is now supporting Estonia's important role in the NATO air defense infrastructure," said Philippe Duhamel, chief executive officer of ThalesRaytheonSystems.
"The new radar system will bring the country an operational long-range air surveillance capability and improved detection performance against a broad array of modern threats."