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The U.S. Navy Diving Manual is a very complete reference on diving based on the extensive research and experience of the U.S. Navy. The manual contains major sections covering rebreathers, no-decompression diving, open-circuit SCUBA, surface-supplied diving, the diving environment, Navy dive procedures, physics, physiology and recompression chamber operation. The U.S. Navy Diving Manual underwent some significant updates with the revisions issued in 2008 and again in 2016. The most recent 2018 revision 7A includes, among other things, updates to diver in-water rescue and accident management recommendations.
Although much of the information is interesting, it may have limited application to your recreational diving. Still, recreational diving has some of its roots in the almost 1000 pages of this large document. Best of all, it's available at no charge because it was developed with taxpayer funds. You can download the U.S. Navy Diving Manual, current revision as a PDF format document from the Navy's diving publications web page. There are some other useful documents on their website such as "Navy Diving Supervisor’s Guide To the Nontechnical Skills Required for Safe and Productive Diving Operations".