The first international connection to ARPANET was made in 1973.
The connection used a transatlantic satellite link between ARPANET in the United States and the Norwegian Seismic Array (NORSAR). Traffic then traveled through Sweden’s Tanum Earth Station and onward over a terrestrial circuit to a Terminal Interface Processor at University College London, where Peter Kirstein’s research group operated.
This milestone mattered because ARPANET was no longer limited to American research institutions. The UCL gateway also linked ARPANET with British academic networks, creating an early example of international resource sharing between separate computer networks.
A common mix-up is 1969, the year ARPANET’s first four domestic nodes were connected, or 1972, when the network was publicly demonstrated at the International Conference on Computer Communications. Those dates describe earlier milestones; the first international connection itself came in 1973.