NATO began to develop a capability for its fleet of Boeing E-3A Airborne Warning and Control System (AWACS) surveillance aircraft after they are retired around 2035. Member nations of the organization signed an agreement on 15 February to commence the relevant studies. NATO Secretary General Jens Stoltenberg stated that NATO would carefully examine many alternatives, including their costs, in order to inform which direction NATO would take in the future. He added that the AWACS mission could be fulfilled by a mix of air, ground and space systems in the future.