To create such a network the Military setup a project called 'Advanced Research Project Administration (ARPA). The basis of the development was that each computer would have a unique address stored in a database each computer on the network would have access to a copy of this data, so each computer knows where all the others are, in relationship to each other this gives an overall 'map' of the network. Thus if a computer did not respond to a message it was not used to send information, and the message would be sent via another responsive computer.
The ARPA got this type of network up and running, and called it 'ARPAnet' but there was still some improvements that were required, for help with this academic sites were allowed on to the network to study its operation and solve problems, slowly the Universities found the network to be of great benefit to them for sharing information, they help develop the protocols that are used on the internet today and it has grown at an accelerating rate. The Military (department of Defence) eventually disconnected themselves from the main internet and started up their 'MILNET' internal Network.
Communication between 'A' and 'H' Computers.
Communications between 'A' and 'H' Computers