The Internet is now one of the most important technologies in human history. Billions of people use it every day to communicate, work, study, shop, watch videos, send messages, play games, and access information.
But the Internet had a very different beginning.
There were no smartphones, websites, social media platforms, search engines, Wi-Fi networks, or modern web browsers when the first message traveled across the early network that eventually helped lead to today’s Internet.
Instead, on October 29, 1969, researchers at the University of California, Los Angeles (UCLA) attempted to send a simple computer command to another computer more than 300 miles away at the Stanford Research Institute (SRI) in Northern California.
They wanted to send the word:
LOGIN
Something went wrong.
The system crashed after only two letters had been transmitted.
Those two letters were:
LO
That accidental “LO” became one of the most famous moments in Internet history.
UCLA records identify October 29, 1969, as the date when the first host-to-host message was sent over ARPANET, the network that became a major predecessor of the modern Internet.
But what exactly happened that night?
Who sent the message?
Why were they sending it?
What computers were involved?
Why did the system crash?
And was “LO” really the first Internet message?
This article explores the complete story.
What Was the First Internet Message?
The first message sent between two computers over ARPANET was:
“LO”
However, “LO” was not the message the researchers intended to send.
Their goal was to send the command:
LOGIN
The researchers wanted the UCLA computer to connect to the computer at the Stanford Research Institute.
They began typing the command one character at a time.
The first character, L, successfully reached SRI.
The second character, O, also arrived.
When the third character, G, was transmitted, the receiving system crashed.
As a result, the first successful host-to-host transmission consisted of only:
LO
The system was repaired, and the complete login command was successfully transmitted later that night. Leonard Kleinrock’s historical account records the first transmission at approximately 10:30 p.m. on October 29, 1969.
Was “LO” Really the First Internet Message?
There is an important historical distinction here.
When people say “the first Internet message,” they are usually referring to the first host-to-host message sent over ARPANET, the predecessor to today’s Internet.
Strictly speaking, the global Internet as we know it did not yet exist in 1969.
ARPANET was an early packet-switched research network.
The modern Internet developed over the following decades through technologies and networks including:
- ARPANET
- TCP/IP
- NSFNET
- Domain Name System
- Internet service providers
- The World Wide Web
- Commercial networks
- Broadband
- Mobile Internet
Therefore, it is more historically precise to say that “LO” was the first host-to-host message sent over ARPANET, rather than claiming that somebody sent a message over today’s Internet in 1969.
Nevertheless, ARPANET was one of the most important foundations of the Internet.
When Was the First Internet Message Sent?
The historic transmission occurred on:
October 29, 1969
The time was approximately:
10:30 p.m. Pacific Time
The message traveled from:
UCLA in Los Angeles
to:
Stanford Research Institute in Menlo Park, California.
UCLA’s own historical records identify the event as the first message sent over ARPANET.
The two institutions were hundreds of miles apart.
At the time, getting two computers to communicate across such a distance was a major technological achievement.
Where Was the First Message Sent?
The message originated at UCLA’s Boelter Hall.
More specifically, the researchers were working in Room 3420, where Leonard Kleinrock’s research group was based.
Today, the location is remembered as an important site in Internet history.
UCLA has preserved the story of the event and identifies Room 3420 as the place from which the first ARPANET message was sent.
At the time, however, the researchers did not know that their experiment would eventually become one of the most famous events in technology history.
They were simply trying to determine whether their new network could work.
Who Sent the First Internet Message?
Several people were involved in the experiment.
One of the most important was Leonard Kleinrock, a UCLA computer scientist whose research helped establish the mathematical foundations of packet-switched networks.
Another key participant was his graduate student and programmer Charley Kline.
At UCLA, Kline operated the computer and attempted to send the login command.
At SRI, Bill Duvall was on the receiving end.
Kleinrock supervised the experiment.
UCLA’s historical record identifies Kleinrock’s team, including Charley Kline, as responsible for the first ARPANET host-to-host transmission.
Who Was Leonard Kleinrock?
Leonard Kleinrock was one of the most important researchers in the development of computer networking.
His work focused heavily on the mathematical theory behind communication networks.
While working as a doctoral student at MIT, Kleinrock developed mathematical approaches for analyzing computer communication and packet-based networks.
His research helped demonstrate that computers could efficiently share communication resources.
This became particularly important when researchers began developing ARPANET.
UCLA describes Kleinrock as a pioneer of the mathematical theory of packet networks on which Internet networking is based.
His work therefore connected two important parts of Internet history:
the theory of packet switching and the first practical ARPANET communication.
Who Was Charley Kline?
Charley Kline was a graduate student and programmer working in Kleinrock’s research group at UCLA.
On the night of October 29, 1969, Kline was responsible for entering the command that would travel across the new network.
He typed the characters:
L
then:
O
then:
G
The first two arrived.
When the third character was transmitted, the system crashed.
The Computer History Museum records the exchange between Kline at UCLA and Bill Duvall at SRI, including the famous moment when the system failed after “G.”
Kline’s role is important because the event was not simply a theoretical demonstration.
A real person was sitting at a computer terminal, entering characters that traveled through a new experimental network.
Who Was Bill Duvall?
Bill Duvall was working at the Stanford Research Institute.
He was positioned at the receiving end of the experiment.
Kline and Duvall communicated over a telephone connection while they tested the new computer network.
This allowed them to confirm whether each character had successfully arrived.
Kline would enter a character and ask Duvall whether he had received it.
Duvall confirmed the arrival of the first character.
Then the second.
When Kline entered the third character, the receiving system crashed.
Kleinrock’s own account describes this exchange and the resulting failure.
Why Were They Trying to Send “LOGIN”?
The goal was not to create a historical message.
The researchers were testing a practical capability of the new network.
They wanted to use the UCLA computer to log into the computer at SRI.
The intended command was:
LOGIN
The system at SRI was designed to complete the command after receiving the necessary characters.
So the researchers started transmitting:
L
O
G
…
But they never initially reached the rest of the word.
The receiving system failed after the “G” was sent.
Therefore, the first successful message became:
LO
What Happened When They Sent the “L”?
The experiment began normally.
Kline entered the letter:
L
The character traveled through the ARPANET connection to SRI.
Duvall confirmed that he received it.
This was already an important moment.
Two computers located hundreds of miles apart had successfully exchanged information through the new network.
What Happened When They Sent the “O”?
The second character was:
O
Again, it successfully traveled from UCLA to SRI.
Duvall confirmed its arrival.
The researchers now had:
LO
Everything seemed to be working.
The next step was to send the letter:
G
Why Did the System Crash?
When Kline entered the G, the system at SRI crashed.
The exact technical circumstances involved a problem in the software running on the SRI host computer.
This is an important detail because the failure was not caused by the basic idea of packet switching itself suddenly becoming impossible.
The network had successfully transmitted the first two characters.
The problem was associated with the host system and its software.
After the failure was identified and corrected, the researchers were able to complete the login successfully.
Kleinrock’s account states that the full login was achieved about an hour later.
Was “LO” Planned?
No.
This is one of the most interesting parts of the story.
The researchers did not intentionally choose “LO” as the first message.
They wanted to send:
LOGIN
The two-letter message was created by an accidental system failure.
Leonard Kleinrock later pointed out that “LO” seemed almost prophetic because it could be interpreted as:
“Lo and behold.”
UCLA has repeatedly highlighted this coincidence in its historical accounts of the event.
Of course, the researchers did not plan this meaning.
It became significant only after the event.
What Was ARPANET?
To understand why the message mattered, it is necessary to understand ARPANET.
ARPANET stood for:
Advanced Research Projects Agency Network
It was developed under the U.S. government’s Advanced Research Projects Agency, later known as DARPA.
The project aimed to connect computers at research institutions.
Researchers wanted to allow computers and people at different locations to communicate and share resources.
ARPANET used packet-switching technology.
Instead of requiring one continuous communication circuit, information could be divided into packets and transmitted through the network.
This was a major change in computer networking.
The First ARPANET Nodes
In 1969, ARPANET initially connected four major research sites.
They were:
- UCLA
- Stanford Research Institute
- University of California, Santa Barbara
- University of Utah
UCLA was the first node.
SRI became the second.
The first host-to-host connection between UCLA and SRI occurred on October 29, 1969. The Computer History Museum also records the handwritten UCLA logs showing the first connection.
The network would later expand to additional institutions.
What Was the IMP?
The computers on ARPANET did not simply connect directly to each other.
A special networking device called an Interface Message Processor, or IMP, was used.
The IMP handled communication between the host computer and the packet-switched network.
Modern readers can think of an IMP as an early predecessor to certain types of networking equipment, although it was not identical to today’s routers.
UCLA’s historical material identifies the IMP as an important part of the first ARPANET connection.
The first IMP arrived at UCLA in August 1969.
It was connected to UCLA’s host computer shortly afterward.
A second IMP was then installed at SRI.
The two IMPs were connected by a dedicated communication link.
This created the basic network path used for the historic test.
How the First Message Traveled
The process can be simplified like this:
UCLA Computer
↓
UCLA IMP
↓
ARPANET communication link
↓
SRI IMP
↓
SRI Computer
The researchers entered characters on the UCLA computer.
The information was processed and passed through the IMP.
It traveled across the communication link.
The SRI IMP delivered the information to the SRI host computer.
This demonstrated that computers could communicate across a packet-switched network.
How Fast Was the Connection?
Today’s Internet connections can transfer enormous amounts of data in seconds.
The original ARPANET connection was dramatically slower by modern standards.
The early UCLA-to-SRI link operated at approximately 50 kilobits per second.
That may sound extremely slow today, but it was a significant technical achievement in 1969.
The purpose was not to stream high-definition video or download huge files.
The researchers were proving that computers could communicate across a network.
Why Was the First Message So Important?
The message itself was extremely small.
Only two characters were successfully transmitted during the first attempt.
So why does it matter?
Because the importance was not in the content.
The importance was in what the transmission proved.
The experiment demonstrated that:
- A computer at UCLA could communicate with a computer at SRI.
- Packet-switched networking could work in practice.
- Geographically separated computers could exchange information.
- ARPANET could function as a real computer network.
- Researchers could begin experimenting with remote computer communication.
This was the beginning of a much larger technological development.
The First Message Was Not an Email
Another common misunderstanding is that “LO” was the first email.
It was not.
The first ARPANET message was a host-to-host login attempt.
Email came later.
Ray Tomlinson is widely credited with developing the first networked email system on ARPANET in 1971 and introducing the use of the @ symbol to separate the user’s name from the computer or host.
Therefore:
First ARPANET host-to-host message: “LO”
First network email: developed later, in 1971
These were different milestones.
The First Message Was Not a Website
There was also no website involved.
The World Wide Web did not exist in 1969.
Tim Berners-Lee would propose the Web at CERN about two decades later, in 1989.
The first website would appear in the early 1990s.
Therefore, the 1969 event was much more fundamental.
It involved computers communicating directly across an experimental network.
The First Message Was Not Sent From a Modern Computer
The computers involved were very different from today’s devices.
The UCLA host was an SDS Sigma 7 computer.
The SRI host was an SDS 940.
These were large computer systems compared with modern smartphones and laptops.
Kleinrock’s historical account specifically identifies the UCLA SDS Sigma-7 and SRI SDS 940 as the host machines involved.
They had nowhere near the convenience, speed, storage, or user interface of modern computers.
What Did Computers Look Like in 1969?
Computers in the 1960s were generally large, expensive machines.
They were often housed in dedicated rooms or facilities.
They were not personal devices.
A normal person could not simply purchase a laptop and connect to the Internet.
Computing was largely concentrated in:
- Universities
- Government agencies
- Research laboratories
- Large companies
- Military organizations
This makes the later growth of the Internet even more remarkable.
The technology moved from a small experimental network connecting research institutions to a global communication system.
What Happened After “LO”?
After the system crashed, the researchers diagnosed and corrected the problem.
They then attempted the login again.
This time, the complete command worked.
The successful connection proved that the system could perform the intended task.
The Computer History Museum describes the first login as failing and the next attempt as succeeding.
The researchers had therefore accomplished their immediate objective.
But the larger significance of the experiment would only become clear over the following decades.
ARPANET Continued to Grow
The first ARPANET connection was only the beginning.
More computers and research institutions were added to the network.
Researchers experimented with:
- File transfer
- Remote computer access
- Network protocols
- Resource sharing
- Network management
- Distributed computing
As the network grew, new technical challenges appeared.
One major challenge was figuring out how different networks could communicate.
That eventually contributed to the development of TCP/IP.
From ARPANET to the Internet
The path from “LO” to today’s Internet was not immediate.
There were many important steps.
A simplified timeline looks like this:
1969 — ARPANET first host-to-host message
↓
1970s — ARPANET expands
↓
1971 — Network email develops
↓
1970s — TCP/IP development
↓
1983 — ARPANET adopts TCP/IP
↓
1980s — More networks become interconnected
↓
1990 — ARPANET is retired
↓
1990s — World Wide Web and commercial Internet expand
↓
2000s — Broadband and Web 2.0
↓
2010s — Smartphones and mobile Internet
↓
2020s — Cloud computing, AI, IoT and increasingly connected services
The Internet became what it is today through decades of development rather than one single event.
Why October 29, 1969 Is Remembered
October 29, 1969 is remembered because it represents a clear moment when two distant host computers successfully communicated over ARPANET.
UCLA has described the event as the beginning of a new connected era.
It was a small experiment with enormous consequences.
The researchers were not launching a global social network.
They were not creating online shopping.
They were not building YouTube.
They were not designing smartphones.
They were testing a new way for computers to communicate.
Yet their work eventually became part of the technological foundation for all of those things.
What Made the Experiment Revolutionary?
The revolutionary idea was not simply sending the word “LO.”
People had communicated electronically before 1969.
The important innovation was the ability to connect computers through a packet-switched network.
Computers could potentially:
- Share information
- Share resources
- Access remote systems
- Communicate with other computers
- Exchange files
- Become part of a larger network
This introduced a completely new model of computing.
Instead of thinking about computers as isolated machines, researchers could begin thinking about them as parts of a network.
The Role of Packet Switching
The success of the first ARPANET message depended heavily on packet-switching technology.
Packet switching breaks data into smaller units and allows network infrastructure to carry information from different users and systems.
This was particularly useful for computer communication because computer traffic tends to occur in bursts.
The work of researchers such as Leonard Kleinrock, Paul Baran, and Donald Davies contributed to the development of the ideas that made packet-switched networking possible.
The first ARPANET connection therefore represents not only a communication milestone but also an important demonstration of packet networking.
The First Internet Message and Today's Internet
It is fascinating to compare the 1969 experiment with the modern Internet.
In 1969:
- Two computers were connected.
- The network had only a handful of nodes.
- The connection was experimental.
- The first message contained two successful characters.
- Access was limited to research institutions.
Today:
- Billions of devices can communicate.
- Websites are accessible worldwide.
- Smartphones connect wirelessly.
- Cloud data centers operate across continents.
- People communicate instantly through messaging applications.
- Video can be streamed around the world.
- Businesses operate online.
- Artificial intelligence services use global networks.
The basic idea of connecting computers has therefore expanded on an extraordinary scale.
Interesting Facts About the First Internet Message
1. The message was supposed to be “LOGIN”
The researchers were trying to establish a remote login.
2. Only “LO” initially arrived
The system failed before the complete command could be transmitted.
3. “LO” was accidental
The researchers did not deliberately choose the two-letter message.
4. The full login worked later
The system was repaired and the intended command was successfully completed.
5. The transmission happened in 1969
This was decades before the modern Web, smartphones, and social media.
6. The experiment involved UCLA and SRI
The first host-to-host transmission traveled between these two institutions.
7. Leonard Kleinrock supervised the experiment
He was one of the major researchers involved in the development of packet-network theory.
8. Charley Kline typed the message
He was the UCLA programmer who entered the command.
9. Bill Duvall received it at SRI
He was on the receiving side of the experiment.
10. “LO” became a symbol of Internet history
The accidental message is now one of the most recognizable moments in the story of the Internet.
Timeline of the First Internet Message
| Date | Event |
|---|---|
| August 1969 | First ARPANET IMP arrives at UCLA |
| September 1969 | UCLA host computer is connected to the IMP |
| October 1969 | Second ARPANET node is established at SRI |
| October 29, 1969 | First host-to-host ARPANET message is transmitted |
| October 29, 1969 | “LO” successfully arrives at SRI |
| Later that night | Full “LOGIN” command successfully transmitted |
| 1970 | ARPANET continues expanding |
| 1971 | Network email becomes an important ARPANET application |
| 1970s | TCP/IP is developed |
| 1983 | ARPANET transitions to TCP/IP |
| 1990s | World Wide Web and commercial Internet adoption accelerate |
The dates surrounding the first connection and transmission are documented in UCLA’s historical material and Leonard Kleinrock’s own account.
Frequently Asked Questions
What was the first message sent over the Internet?
The first host-to-host message sent over ARPANET was “LO.” It was supposed to be the beginning of the word “LOGIN,” but the receiving system crashed after the first two letters.
When was the first Internet message sent?
It was sent on October 29, 1969, at approximately 10:30 p.m.
Who sent the first Internet message?
A team led by UCLA computer scientist Leonard Kleinrock sent the message. Graduate student and programmer Charley Kline operated the UCLA computer, while Bill Duvall was at SRI.
Where was the first Internet message sent?
It was sent from UCLA in Los Angeles to the Stanford Research Institute in Menlo Park, California, over ARPANET.
Why was the message “LO”?
It was not intentionally chosen. The researchers were trying to send “LOGIN,” but the system crashed after “LO” had been transmitted.
Was “LO” the first email?
No. It was the first host-to-host ARPANET message. Network email was developed later, with Ray Tomlinson’s work in 1971 becoming a major milestone.
Was the World Wide Web involved?
No. The World Wide Web had not yet been invented. Tim Berners-Lee proposed the Web at CERN in 1989.
Did the Internet exist in 1969?
ARPANET existed in 1969 and became an important predecessor to the modern Internet. The global Internet developed over subsequent decades.
What computer received the first message?
The receiving host at SRI was an SDS 940 computer.
What happened after the first message?
The researchers fixed the problem and successfully completed the intended login. ARPANET then continued to expand and evolve.
Why the “LO” Story Still Matters
It is easy to look at the first Internet message and think that “LO” was insignificant.
After all, it was only two letters.
But technological revolutions often begin with small experiments.
The people at UCLA and SRI were not trying to create the Internet as we know it today.
They were testing whether computers could communicate across a new type of network.
Their experiment worked.
The first attempt failed partially, but the researchers learned from the failure and completed the login later.
That small experiment demonstrated a powerful idea:
Computers could communicate across a network, even when they were hundreds of miles apart.
That idea would eventually become the foundation for a connected world.
Conclusion
The first Internet message was not a long email, an important announcement, or a carefully written sentence.
It was simply:
LO
On October 29, 1969, researchers at UCLA attempted to send the command “LOGIN” to a computer at the Stanford Research Institute using ARPANET.
The system crashed after the first two letters.
Yet those two letters became a historic milestone.
The experiment demonstrated that computers could communicate across a packet-switched network. It helped prove the practical potential of ARPANET and became an important early step toward the Internet.
From that tiny “LO” came decades of technological development.
ARPANET expanded.
Email emerged.
TCP/IP connected different networks.
NSFNET helped expand Internet infrastructure.
The World Wide Web made Internet information accessible through browsers.
Commercial Internet providers brought connectivity to homes.
Broadband made connections faster.
Smartphones brought the Internet into people’s pockets.
Cloud computing connected users to enormous remote data centers.
Today, billions of people depend on technologies that can trace part of their history back to experiments like the one conducted at UCLA and SRI in 1969.
The first message was tiny.
Its consequences were enormous.
And that is what makes “LO” one of the most important two-letter messages ever sent.
