Why ARPANET’s first host-to-host message stopped at LO

On October 29, 1969, UCLA computer science student Charley Kline tried to log in remotely to a computer at the Stanford Research Institute. The first two letters arrived: “L” and “O.” When Kline sent “G,” the system crashed. The team completed the login about an hour later. That small failure became a useful origin story for ARPANET. The intended command was simply “LOGIN”; “LO” was an accident of timing, not a planned message or a prophecy. UCLA professor Leonard Kleinrock later recalled the attempt, while the surviving UCLA IMP log records a 10:30 p.m. host-to-host exchange with SRI and a later “host dead” message. The log itself does not spell out “LO”; that detail comes from Kleinrock’s account. It is often called the first Internet message, but the careful description is ARPANET’s first host-to-host message. ARPANET was an early packet-switching network and a major precursor to the Internet. The Internet as an interconnected network took shape later, when TCP/IP let separate networks communicate in 1983. The image is a 2011 photograph of the surviving UCLA IMP log, not a picture of the 1969 session. Photo: Andrew “FastLizard4” Adams, uploaded by Rybec, CC BY-SA 2.0 ([image and license](https://commons.wikimedia.org/wiki/File:The_IMP_Log_The_Very_First_Message_Sent_on_the_Internet_(6293913865).jpg)). [Kleinrock’s account](https://www.icann.org/en/blogs/details/the-first-message-transmission-29-10-2019-en) · [UCLA log](https://www.lk.cs.ucla.edu/internet_first_words.html) · [DARPA history of ARPANET](https://www.darpa.mil/news/features/arpanet). ~Internet ~Technology