How did banks transmit international payment instructions before SWIFT existed?

They used a telex machine, it was like a real-time modem/typewriter that was connected and it transmitted messages in real-time.

Based on the origination number (Bank’s telex code), ledgers were then adjusted.

There was a specific code and format that as utilized and the receiving party then did the adjustment to their ledger balances and made payments.

The word TT rate comes from “telegraphic transfer”.

This is what the machine looked like:

Here is a modern version that is working. The ticket tape going through it is the pre-typed message being read off this tape.

https://www.youtube.com/watch?v=...