The ASSIST database is the official source for specifications and standards used by the US Department of Defense. Indexed documents include current and historical military and federal standards and specifications. The ASSIST document database houses over 180,000 PDF files associated with about 82,000 of the approximately 111,000 indexed documents. (Updates vary)
What is the website address?
US DOD provides with a tool called ASSIST QUICK SEARCH for searching for any of the US military standards. ASSIST website has the historic versions of the standards. All can be downloaded free of charge.
https://quicksearch.dla.mil/qsSearch.aspx is the link for Assist website quick search tool.
Why US DOD does not charge fee for standards?
US DOD assumes that the cost of the effort for developing standards is met with the tax dollars paid by the people. That is probably the reason why these products are free for anyone. The intended audience therefor is probably the US people.