RADC was Rome Air Development Center (from memory at the time; I got on the network in the fall of '72 as a frosh at HARV-10), a big funder of ARPA-related research.

I'm pretty sure RADC were the funding sources for much of the CS research going on at the Harvard CRCT [Center for Research in Computing Technology] in those days. My advisor, Tom Cheatham (RIP), was the head of the CRCT and the PI for many of the funded research programs. (Great man.)

All from memory, the less obvious names:

MIT: LCS, AI, Arch. Machine group, Multics, etc.

Harvard: CRCT with a few machines (PDP-10, -1, etc.)

BBN: contractor that developed the original ARPANET technology

Aberdeen and Belvoir: I believe Army testing grounds

NBS: National Bureau of Standards

MITRE (Corp)

Lincoln (Labs)

LBL (Lawrence Berkeley Labs)

Xerox (MAXC was PARC's home-made PDP-10 clone)

SDC (Software Dev Corp)

We had fun back in the "open days" when most systems had open guest accounts, telnetting from machine to machine to see how many "miles" we could go before the whole thing broke down.

(Fun factoid: back in the early days of email, the mail delivery mechanism was anonymous FTP to append to your recipient's mailbox file.)

Eventually (I'm vaguely remembering by 1973-74) there were enough troubles with vandals that all the open accounts were turned off. (I remember watching a TTY where Harv-10 was logging all typing from guest users, see what mischief they were up to.)

"Those were the days, my friend, we thought they'd never end..."