In 2013, then-Secretary of Defense Leon Panetta warned that "budget uncertainty could prompt the most significant military readiness crisis in more than a decade." Four years later, observers are debating whether a readiness crisis has indeed come to pass, disagreeing on how ready the U.S. military currently is, and debating what steps should be taken to improve military readiness. Little consensus has emerged, partly because the term readiness is not used in the same way by all observers or participants in the debate. Recently, DOD has made readiness a central justification for increased funding as necessary to address "immediate and serious readiness challenges." DOD's funding request for FY2017 favors preparations that improve the military's capability in future years, like buying new equipment, whereas the FY2018 budget request favors more immediate training and maintenance shortfalls. In both cases, however, the request is justified in terms of improving readiness, contributing to the confusion by using the term readiness in different ways. As these examples show, "readiness" is used both in a narrow sense to discuss the military's current level of training and the status of its maintenance, and in a broader sense to describe the military's overall capability, which includes how large the force should be and what kinds of weapons it should have, even if those changes will not take effect for several years. To help Congress understand the different uses of the term readiness, this report explores these two common uses of the term with examples, attempts to clarify the two uses, and discusses why it is so difficult to define the term. It also provides historical examples of when the two uses of the term readiness received different priorities than they do today. The report then considers how the different uses of the term readiness inform how Congress might evaluate certain issues: Is there a readiness crisis? What should the U.S. military be ready for? How should readiness be measured? How does the FY2018 budget request affect the U.S. military's readiness? While this report discusses how differing uses of the term readiness affect the debate, it does not evaluate the current state of the U.S. military's readiness or provide a conclusive definition of readiness. Despite many definitions of readiness, CRS has identified two principal uses of the term. One, readiness has been used to refer in a broad sense to whether U.S. military forces are able to do what the nation asks of them. In this sense, readiness encompasses almost every aspect of the military. For example, Lieutenant General Joseph Anderson of the U.S. Army testified Readiness is the capability of our forces to conduct a full range of military operations to defeat all enemies, regardless of the threats that they pose. It is generated through manning, training and equipping our units and leader development. Similarly, in 2014, retired General Gordon Sullivan used readiness in this broad sense, tying readiness largely to the size of the force: More than 100 years ago, the siren song of reductions in defense manpower was luring the unsuspecting onto the shoals of unpreparedness for future conflict ... This cycle of readiness followed by unpreparedness has repeated itself all too often throughout our history. Two, readiness has also been cast more narrowly as only one component of what makes military forces capable. In this sense, readiness is parallel with other aspects of the military, like force structure and modernization (which usually refer, respectively, to the size of the military and the sophistication of its weaponry). For example, General Stephen Wilson of the U.S. Air Force, in testimony, used readiness in the latter sense: ...current budget levels require the Air Force to continue making difficult tradeoffs between force structure, readiness , and modernization. Two years earlier, General Norton Schwartz, then-Chief of Staff of the Air Force, also used readiness in its narrow sense, parallel with other components: When we speak of operational effectiveness, we are talking about securing the appropriate balance of three separate but very closely related dimensions— readiness , modernization, and force structure—that mutually affect each other, and must be carefully integrated together. For other uses of the term beyond these, see the Appendix . Speakers often seek to clarify in which of the two principal uses they are describing readiness by applying a variety of adjectives. Richard Betts in his 1995 book on readiness distinguished them by calling the broader use "structural readiness," and the narrower conception "operational readiness." More recently, General Glenn Walters of the U.S. Marine Corps used "institutional readiness" to invoke the broader use and "unit readiness" to invoke the narrower use: Marine Corps institutional readiness is built upon five pillars: Unit Readiness ; Capability and Capacity to Meet Joint Force Requirements; High Quality People; Installation Capability; and Equipment Modernization. Brad Carson and Morgan Plummer, former DOD officials, distinguished the two uses in the following terms: [A] ... more limited meaning that might be called ' strategic readiness ' : the ability of the military to accomplish the tasks demanded by the national command authority. This is the implicit definition used regularly in congressional testimony and public commentary. ... [Another] definition of readiness, still more parsimonious, might be called ' force readiness ' : the resource ratings of units, their ability to perform generic combat tasks, and, to a lesser extent, the ability of combatant commands to execute set-piece operational plans. These attempts to clarify the term "readiness" acknowledge that both uses embody accepted concepts: the broader use capturing the military's ability to accomplish its overall goals and the narrower use capturing the military's ability when its size and type of weaponry are held steady. These attempts also highlight that the two concepts are interdependent, as illustrated by DOD's official definition of readiness. DOD's official doctrinal definition of readiness is The ability of military forces to fight and meet the demands of assigned missions. This definition, however, does not resolve the confusing use of the term. If "military forces" is assumed to hold the size and composition of the forces steady, this definition would imply the narrow use of readiness. Since one can posit military forces changing in size and composition to "meet the demands of assigned missions," however, the definition does not rule out the broader use. DOD also doctrinally defines "operational readiness" as The capability of a unit/formation, ship, weapon system, or equipment to perform the missions or functions for which it is organized or designed. The two DOD definitions seemingly follow the two principal uses of readiness: the broader and the narrower. But as shown by the examples above, many users do not consistently follow the doctrinal definitions, invoking the word readiness , unmodified, for both senses of the term. The two uses do not lend themselves to strict definition because they are interdependent: greater readiness in the narrow sense, such as better trained personnel, may offset the disadvantages of a smaller or a less technologically sophisticated force, depending on what task the military is executing. Alternatively, the military could be ready in the broader sense because its size and the sophistication of its weapons make up for shortfalls in such areas as training or how often a unit has used its equipment before experiencing combat. These difficulties extend to what budget lines support "readiness." No authoritative list exists. If, however, readiness is used in the narrow sense—as one piece of what makes the military able—it can be contrasted against other pieces, such as buying new equipment. In this sense, the operations and maintenance (O&M) appropriations title, which must be spent sooner than other parts of the budget, can be considered a proxy for narrow readiness funding as opposed to other appropriations such as the procurement appropriations title, which can be spent over multiple years. O&M as an entire appropriations title, however, may not be the best way to measure readiness in the narrow sense. The full title includes funding for activities often not associated with readiness, even a narrow sense, like funding Junior ROTC for high school students, real estate management, and enterprise communications networks. A potentially better way to capture the narrow concept of readiness is to focus on Budget Activity 1, Operating Forces, which includes only the O&M funding for operational units of the military services. Tables displayed later in this report will show all three categories. While these accounts provide rough proxies for readiness in the narrower and broader sense, they are not exclusive to either sense, thus preventing any absolute judgments. How the term readiness is used is important to Congress because DOD has made readiness central in its justifications for increased funding. The Trump Administration released a National Security Presidential Memorandum on January 27, 2017 directing DOD to conduct a 30-day readiness review and concurrently to develop a FY2017 budget amendment for military readiness and other subjects. Secretary of Defense Mattis then issued a memorandum on January 31, 2017 stating the Administration's priorities in "strengthening the U.S. Armed Forces" would be approached "in a campaign of three phases:" First, addressing "immediate and serious readiness challenges" in a FY2017 budget amendment request; Second, refining and improving the FY2018 budget request to "focus on balancing the program, addressing pressing programmatic shortfalls, while continuing to rebuild readiness;" and Third, preparing the FY2019 budget request and five-year defense program throughout calendar year 2017. The FY2019 request is to be informed by the 2018 National Defense Strategy, which DOD was to begin in spring 2017, and "inform our targets for force structure growth." The Secretary's memorandum also emphasized enhancing lethality against high-end competitors and effectiveness against a broad spectrum of potential threats. The third phase did not mention readiness. DOD fulfilled phase one of its approach when it released its request for additional FY2017 appropriations on March 16, 2017. The FY2017 budget amendment seems to blur the first two phases of the DOD Secretary's memorandum by invoking both the broader and narrower uses of "readiness."