"Significant formal investigators of systems engineering have included Goode and Machol (1957), A.D. Hall (1962), Chestnut (1965, 1967), Sage (1977a,b), and Blanchard and Fabrycky (1981), whose descriptions span 24 years. Although each investigator has approached this subject with a slightly different orientation, all have dealt with defining the elements of systems engineering and various methods of approaching the implementation of these elements. In addition, the US government, through its development and acquisition of large-scale systems over the years, has addressed all aspects of systems engineering. These have been documented in government- sponsored texts (e.g.. System Engineering Management Guide 1986) as well as numerous related standards, directives and handbooks, especially those printed by the US Department of Defense."