Final answer:
Ground Control Intercept (GCI) service is the answer to the question which combines air traffic control with combat direction functions, providing surveillance, identification, and guidance in a military defense context.
Step-by-step explanation:
The service described in the question combines air traffic control with the provision of combat direction and is mission oriented. The correct answer is a. Ground Control Intercept (GCI) service. GCI is a service within the air defense system which performs surveillance, identification, control, and guidance functions. This service uses radar and communication systems to provide assistance to intercept hostile aircraft by directing fighter aircraft towards them. It is often used by military forces to defend airspace by tracking and intercepting potential threats such as enemy aircraft and missiles. Examples of this service might include directing fighter jets to intercept enemy bombers, or guiding surface-to-air missiles to engage with incoming targets. Notably, the context of confirmed and possible surface-to-air missile sites, support facilities for processing equipment, and airfields with military aircraft like MIGs is indicative of the air defense environment in which GCI is typically employed.