Citing the threat posed by North Korean missiles, the U.S. military has sent the first elements of its Terminal High Altitude Area Defense (THAAD) system to South Korea. China has opposed the move, which has also drawn mixed reactions in South Korea.

The shipment landed in the night of March 6, with a C-17 cargo aircraft unloading two large mobile launchers on the tarmac at Yongsan Garrison in Seoul. The plan to install a THAAD system on the Korean peninsula was laid out by the U.S. and South Korea last summer.

“China says that its main concern is that the system’s radar could be used to spy on China’s military, and the missiles could possibly counter China’s nuclear deterrent.” NPR’s Anthony Kuhn reports from Beijing.

The U.S. is calling the system’s deployment a defensive measure, saying that it is “aimed solely at” defending against missiles from North Korea.