In the study, the duration of training of specialists in the branches of the armed forces of a formation (unit) refers to the amount of training time or the number of training hours required to achieve the required level of training of specialists in the relevant categories (profiles), primarily those that determine the combat capability of the formation (unit). The current conditions of armed struggle place increased demands on the level of training of troops (forces). At the same time, during a special period, this training can be carried out under conditions of significant resource, including time, constraints, which requires military command and control bodies (commanders) to take a balanced and comprehensively justified approach to planning training and building the training process of troops (forces). Thus, the experience of combat operations once again confirms the need to address one of the most important and problematic issues - to ensure that the amount of training time allocated for the training of specialists in formations (units) and in training centres (schools) meets real needs. Failure to address this issue has a negative impact on the development of the knowledge, skills, physical and psychological qualities required in a combat situation, and thus on the combat capability of the unit. At present, in units and training centres (schools), the amount of training time required for certain military specialities (positions) is determined mainly based on military experience, by comparing different forms and methods of training, and without the necessary analytical justification. Therefore, the relevance of this study is precisely due to the need to scientifically substantiate the amount of training time that would ensure both the required level of training of specialists in the relevant categories (profiles) and the appropriate level of training and combat capability of units of the branches of the military and the formation (unit) as a whole. The purpose of the article is to outline the methodological aspects of substantiating the duration of training of specialists in the branches of the military forces of a formation (unit). With the help of the above methodological aspects, it is possible to analytically express the process of training specialists of any category (profile) through a function of the type, which characterises the dependence of the achieved level of training of these specialists on the number of training hours during which servicemen learn a certain amount of information - acquire the necessary knowledge, skills and abilities. Graphically, the function can be represented as a -shaped curve thatcharacterises the dynamics of the educational process - the initial and main periods of training. Based on the results of the study of the behaviour of the -shaped curve and the position of its inflection point, the law of change in the level of training (training effectiveness) of specialists of a certain i-th category (profile) is formulated, depending on the number of training hours during which they acquire the necessary knowledge, skills and abilities, and the values of the parameters and, which most appropriately reflect the dynamics of the educational process of specialists of any category (profile). The presented law makes it possible to unambiguously determine the required number of training hours to achieve the desired level of training of specialists in the branches of the military forces of a formation (unit), and the dynamics of its behaviour is like the continuous Weibull-Gnidenko probability distribution. The materials of the article are of theoretical value for further scientific research on the problem, as well as practical value - aimed at maintaining (developing) the typical group of capabilities FDR-3 (Training of Military Command and Control Bodies and Troops (Forces)). The practical use of the above methodological aspects will contribute to improving the quality of planning and building the process of training troops (forces), and thus to increasing their combat capability and ability to effectively counter the enemy on the battlefield.