In 1980, System Development Corporation (SDC) delivered software for a modern air defense system (ADS) for a foreign country. Development of the ADS software was a successful SCD project where all products were delivered within budget and within an ambitious 25 month schedule. This paper describes SDC's approach and experience in developing ADS software. SDC's software development approach included the first time use of an off-the-shelf operating system for a major air defense system, the application of a selective set of modern software development techniques, and use of a matrix management structure. SDC's successful application on ADS of a commercial operating system, a higher order language, a Program Design Language, a Program Production Library, structured walk-throughs, structured programming techniques, incremental build implementation and testprocedures, interactive development, and word processing is described. A discussion of the advantages realized and difficulties encountered in the ADS matrix management structure is presented. The paper concludes with a summary of how SDC will develop software on future projects as a result of its experience on ADS.