Bolt Beranek and Newman (BBN) Report #4799 Document entitled 'A History of the ARPANET: The First Decade'. First published in 1981, and detailing early ARPANET engineering, via the March 2015 'The Internet Protocol Journal' (Volume 18, Number 1). Download IPJ back issues and find subscription information at Internet Prorocol Journal.
DARPA has updated it's six month old : An astounding, curated compendium of fascinating data and phenomenal projects. Highly recommended, from Big Data initiatives - Detection and Computational Analysis of Psychological Signals (DCAPS), to Probabilistic Programming for Advanced Machine Learning (PPAML).