closely to IT in the business world. C4 is command, control, communication and computing, S is surveillance and I for intelligence. Radar has a role in S, but doesn't have to be there depending on the mission. Regardless, C4SI or sometimes called C4SRI is for decision support. People work in this field doesn't have to know much about Radar. Also, fyi, C4SI is used mostly in the industry, the US military doesn't use that word much.