They'd created Arpanet in order to log onto remote computers. E-mail was the killer app for 20 years, until the Web came along.
Some people still consider it networking's killerapp.
The goal there was to fill the building with computers, not to fill the nation with computers. Being the network guy, my job there was to connect the computers in the building. I guess it was the world's first laser printer. And it printed a page per second at 500 dots per inch, which is 500x500x8 x 11 per second, which is a lot of bits per second, more than you could send overRS232, which was the networking scheme of the day. We had to build a network for megabits per second, to feed that computer, to keep it running.