Paul Baran of the RAND Corporation produced a study of survivable networks for the U.S. military in the event of nuclear war

The issue of connecting separate physical networks to form one logical network was the first of many problems. Early networks used message switched systems that required rigid routing structures prone to single point of failure. In the 1960s, Paul Baran of the RAND Corporation produced a study of survivable networks for the U.S. military in the event of nuclear war. Information transmitted across Baran's network would be divided into what he called "message blocks". Independently, Donald Davies (National Physical Laboratory, UK), proposed and was the first to put into practice a local area network based on what he called packet switching, the term that would ultimately be adopted. Larry Roberts applied Davies' concepts of packet switching for the ARPANET wide area network, and sought input from Paul Baran. Kleinrock subsequently developed the mathematical theory behind the performance of this technology building on his earlier work on queueing theory.