Raytheon BBN Technologies Corp., Arlington, Virginia, is awarded a $15,773,090 18-month modification to exercise Option One to a previously awarded cost-plus-fixed-fee contract (N66001-20-C-4006) to develop systems and conduct testing for a heterogeneous underwater network to include dynamically reconfigurable architectures that leverage advances in undersea communications and autonomous ocean systems and demonstrate utility at sea with advanced prototypes. Work will be performed at contractor facilities in Cambridge, Massachusetts (75%); Arlington, Virginia (10%); La Jolla, California (5%); Portsmouth, Rhode Island (5%); and at potential government test facilities (5%). The period of performance of option one is from May 27, 2021, through Nov. 26, 2022. Fiscal 2021 research, development, test and evaluation (Department of Defense) funds in the amount of $2,317,846 will be obligated at the time of award, and will not expire at the end of the current fiscal year. This contract was competitively procured via a Defense Advanced Research Projects Agency (DARPA) broad agency announcement solicitation published on the beta.sam.gov and DARPA websites. Seven proposals were received and three were selected for award. Naval Information Warfare Center Pacific, San Diego, California, is the contracting activity (N66001-20-C-4006).