R 041854Z DEC 25 MARADMIN 584/25  MSGID/GENADMIN/DC CDI QUANTICO VA//  SUBJ/PUBLICATION AND AVAILABILITY OF A CONCEPT FOR 21ST CENTURY  AMPHIBIOUS OPERATIONS// REF/A/MSGID: MCO/CMC/YMD: 20231002// NARR/REF A IS MCO 5401.1, CONCEPT GENERATION AND DEVELOPMENT//  POC/A. H. ARMSTRONG/LTCOL/MCWL FUTURES AND CONCEPTS/ [email protected]//  GENTEXT/REMARKS/1. In July 2025, the Commandant of the Marine Corps and the Chief of Naval Operations  approved a 21st Century Concept for Amphibious Operations (21CAO).   This concept is published at the following links:  1.a. Unclassified executive summary:  https:(slash)(slash)usmc.sharepoint-mil.us/sites/DCCDI/SitePages/ Final_Reports.aspx  1.b. Classified concept library: https:(slash)(slash)intelshare. intelink.sgov.gov/sites/cdi/SitePages/FinalReportsLibrary.aspx  2. Background. Naval amphibious operations provide fleet commanders with unique and asymmetric capabilities to deter aggression, respond to crises and contingencies, and conduct combat operations when  necessary. The character of war continues to evolve. The exploitation of additional domains for warfighting purposes and the corresponding  asymmetries directly influence the methods and means of executing  amphibious operations.  3. Purpose. 21CAO describes threat-informed ways and means for  conducting amphibious operations in the anticipated future operating  environment. These missions are required to accomplish Joint Force Maritime Component Commander objectives against strategic  competitors and serve as a hypothesis from which to conduct further  investigation. These methods and means represent an offset to the  asymmetries future adversaries will depend on and serve as a  framework for capability development and force design.  4. Scope and Central Idea. 21CAO describes future amphibious  operations in the 2040-2045 time range. The concept is threat- informed and globally-applicable. The concept’s central idea is that future amphibious operations will contribute to campaigning by  seizing, defending, and denying key maritime terrain to support sea  control and conduct sea denial. 21CAO addresses diversified  amphibious operations including additional types of amphibious  operations, scalable amphibious operations, integrated stand-in force and amphibious operations, streamlined command relationships, and operationalized phasing.  5. Operating Concepts. 21CAO adds to the library of active Marine  Corps and Naval operating concepts:  5a. Littoral Operations in a Contested Environment (LOCE), 2017.  5.b. Concept for Expeditionary Advanced Base Operations (EABO), 2019.  5.c. A Concept for Stand-in Forces (SIF), 2021.  5.d. Concept for Naval and Special Operations Forces Operations  (CNSO), 2023.  5.e. Naval Concept for Distributed Maritime Logistics Operations  (DMLO), 2023.  5.f. Marine Corps Concept for Logistics (MCCL), 2024.  6. Collectively, the family of naval operating concepts is continuing to guide Marine Corps modernization. 7. This MARADMIN is applicable to the Marine Corps Total Force.  8. Release authorized by Lieutenant General Eric E. Austin, Deputy Commandant for Combat Development and Integration.//