---
title: "ARPANET Definition and History | Model Diplomat"
description: "ARPANET was the U.S. Defense Department's network that began in 1969, laying the groundwork for the modern Internet used by researchers and students."
url: "https://modeldiplomat.com/learn/glossary/arpanet"
---

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Model Diplomat Research Team · Last reviewed June 22, 2026

TL;DR

- ARPANET was the packet-switched computer network funded by the U.
- S.
- What is the difference between ARPANET and the Internet?
- Who developed TCP/IP and when was it adopted by ARPANET?
- Which agency funded ARPANET and what was its strategic context?

[Civil Service & Diplomatic Exams](https://modeldiplomat.com/learn/civil-services/glossary)Updated June 22, 2026

ARPANET was the packet-switched computer network funded by the U.S. Defense Department's ARPA that began operating in 1969 and became the technical precursor to the modern Internet.

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## Timeline

1. 29 October 1969

   The network became operational on , when the first host-to-host message was sent from Leonard Kleinrock's laboratory at UCLA to the Stanford Research Institu…

2. 1 January 1983

   On —"flag day"—ARPANET formally switched from NCP to TCP/IP, an event widely regarded as the technical birth of the Internet, since TCP/IP enabled internetwo…

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Example

On 29 October 1969, Leonard Kleinrock's team at UCLA transmitted the first ARPANET message to the Stanford Research Institute, sending "LO" before the system crashed mid-word.

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