RAND Corporation’s National Security Research Division http://www.rand.org/nsrd.html is a treasure trove on most defence-related subjects.

War on the Rocks http://warontherocks.com offers mainly blogs by many well–known strategic commentators.

West Point’s Modern War Institute https://mwi.usma.edu/ offers short essays and blog-type contributions, many of which are quite intelligent.

Center for Strategic & International Studies (CSIS) http://csis.org/category/topics/defense-and-security presents analysis on a valuable wide range of defence subjects.