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Research Questions

  1. What is by, with, and through?
  2. What lessons can be derived from OIR practices and outcomes?

This report, which provides a narrative account of four battles within Operation Inherent Resolve (OIR) and a review of U.S. ground force contributions to those battles, is intended to serve as an operational history and review of warfighting functions as applied to OIR. Although OIR was both a Coalition fight and joint one, the report's focus on U.S. ground forces is meant to address gaps both in analysis and in the common understanding of OIR.

This research was structured according to the operational concept of by, with, and through. This concept refers to the U.S. military's reliance on local partners — either a host nation government or a local surrogate force — to prosecute ground fighting with U.S. support. That support typically encompasses U.S. advising and enablers and could involve U.S. forces accompanying the partner. Although the terminology is familiar to those working in national security, it has yet to be formalized in joint doctrine and there are inconsistencies in its usage. The authors trace the development of the concept and its application in OIR, then analyze how it might be better incorporated into military doctrine.

The authors detail four battles: the counterattacks on Ramadi and on Fallujah, setting the conditions for Mosul, and the urban fight in Mosul. The choice of these operations was made to ensure treatment of the Euphrates and Tigris river valleys where the Islamic State of Iraq and Syria was defeated in Iraq and to cover battles at different points in the overall campaign.

Key Findings

The evolution of the by, with, and through concept over time parallels the broader expansion in the scale, scope, and strategic significance of U.S. efforts to build foreign security forces

  • The U.S. military's practice of training, equipping, advising, and assisting foreign partners long predates the by, with, and through formulation.
  • The concept of "through, with, and by" originated within the U.S. Army Special Forces in the early 1990s.
  • Once incorporated in joint doctrine, the phrase was soon reappropriated beyond the special operations context.
  • In recent years, there has been a push to establish a commonly understood definition of by, with, and through and to develop a core set of its precepts.

OIR has demonstrated that by, with, and, through works as an operational approach and has many virtues

  • There is no substitute for U.S. Army advisers being able to deliver kinetic effects beyond strictly advising. Delivering kinetic effects increases adviser influence and leverage.
  • Improving the Army's by, with, and through capacity will require substantial investments in training and manpower oriented toward the effort.
  • OIR achieved its short-term objective but might not serve as a replicable blueprint for many future operations — particularly in places where the United States lacks deployment history.
  • By, with, and through was a highly effective operational concept for OIR. However, the development of any future doctrine formalizing it should reflect insights from multiple cases.


  • U.S. military and political leadership should resist the temptation to default to a by, with, and through approach in future contingencies in expectation of similar outcomes as OIR.
  • U.S. land forces should prepare for combat even when called on to apply a by, with, and through approach to future operations. The type of warfighting they might be asked to do — close combat attack and delivery of surface fires — introduces less physical risk but is, nonetheless, combat.
  • Future by, with, and through endeavors should prioritize the generation of indigenous combat-ready forces and local ownership of the fight before introducing accelerants, such as surface fires or advising at lower echelons.
  • The by, with, and through concept should not immediately be elevated as a stand-alone mission or activity that warrants the doctrine, organization, training, materiel, leadership and education, personnel, and facilities investments that would accompany such a move. However, should it wish to formalize the by, with, and through concept into doctrine, the Army should (1) socialize this development across the joint force, especially among the services and combatant commands, and (2) harmonize any doctrinal differences in use and interpretation of this concept that currently exist within the conventional Army and among other communities, such as Special Operations Forces.

Research conducted by

The research described in this report was sponsored by the Office of the Deputy Chief of Staff, G-3/5/7, U.S. Army and conducted by the Strategy, Doctrine, and Resources Program within the RAND Arroyo Center.

This report is part of the RAND research report series. RAND reports present research findings and objective analysis that address the challenges facing the public and private sectors. All RAND reports undergo rigorous peer review to ensure high standards for research quality and objectivity.

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