ARPA originally operated the ARPANET under the U.S. Department of Defense. ARPA stood for the Advanced Research Projects Agency, an agency created in 1958 in response to the Soviet Union’s launch of Sputnik.
ARPA funded research into resilient computer communications, and its Information Processing Techniques Office supported the development of packet-switching networks. The first ARPANET nodes connected UCLA, the Stanford Research Institute, UC Santa Barbara, and the University of Utah in 1969.
The agency was renamed DARPA, for Defense Advanced Research Projects Agency, in 1972. It briefly returned to the name ARPA in the 1990s before becoming DARPA again. ARPANET was not the entire modern Internet, but its networking experiments and later adoption of TCP/IP made it a central ancestor of the global network.