The aim of the article is to show the way of adaptation of the military potential of the Crown to the Tatar threat, which first emerged in 1468. In connection with the particular geopolitical situation we present the dissimilarity of military reforms from those in Western Europe. In order to prevent Tatar raids, a standing frontier army (obrona potoczna or Permanent Defense) was formed. In the 1520s, an innovative strategy was developed which involved creating two defense lines with a very deep reconnaissance, 500 kilometers east of Lviv, already on the territory of the Grand Duchy of Lithuania. The consequence of applying the new model of defense was a new type of armed forces developed approximately two decades later, the cossack cavalry. The article presents a phenomenon of the creation a unified, in terms of weaponry, light cavalry, the process of which took place in the 1540s and 50s. Earlier the troops had consisted of soldiers differently equipped and armored and using various horses. Out of this chaos there emerged more unified units, which was the result of experiences of south-east borderline defense. The article emphasizes it was neither commanders-in-chief nor political and governmental factors that played a key role in the tactical innovation was mid-level commanders (starosts, rotmistrzes). It was their experiments with different types of arms that brought about a revolution in the rearmament and uniformity of the cavalry. The paper indicates that the main originator of the transformations was the starost of Bar and Trembowla Bernard Pretwicz. A clear influence of political decisions and strategic concepts on the final transformations in the warfare tactics should be noted.