Sentence:  The cost of developing a major weapon system is now so enormous that the greatest care must be exercised in selecting new <WSD>systems</WSD> for development , in determining the most satisfactory rate of development , and in deciding the proper time at which either to place a system into production or to abandon it . 
Meaning of the word marked with <WSD> tags:  instrumentality that combines interrelated interacting artifacts designed to work as a coherent entity