The British network often described as the first packet-switched network is the NPL network.
Developed at the United Kingdom’s National Physical Laboratory, the NPL network grew from Donald Davies’s 1965 packet-switching work. Davies independently developed the packet-switching concept and chose the word “packet” for the small units into which messages were divided. NPL began building a practical local network in 1968.
Elements of its Mark I network became operational in early 1969, before the first ARPANET node. The network was fully operational in January 1970 and demonstrated that data could be broken into packets, routed through switching nodes, and reassembled at its destination.
The wording can cause confusion because ARPANET is often called the first wide-area packet-switched network. NPL was a local-area network, but it was an earlier operational packet-switching system. Its work influenced ARPANET and later networks, including France’s CYCLADES.