The intended first word transmitted over ARPANET was LOGIN. On 29 October 1969, UCLA student programmer Charley Kline attempted to connect from UCLA’s computer to the Stanford Research Institute’s computer by sending the command “LOGIN.”
The test was conducted under the supervision of computer scientist Leonard Kleinrock. Kline typed the command toward SRI, where Bill Duvall was ready to receive it. The system crashed after only the first two letters, “LO,” had arrived. The operators then restored the connection and successfully completed the login shortly afterward.
This creates an often-repeated historical distinction: LOGIN was the intended message, while LO was the first text actually received in the initial transmission. The question asks for the intended word, making LOGIN the canonical answer. “LO” is a defensible answer only when asking what the first partial transmission contained.
ARPANET was the Advanced Research Projects Agency Network, an early packet-switching network funded by the U.S. government. Its first host-to-host link connected UCLA and SRI, laying important groundwork for the modern Internet.