The reliability of armored systems in combat vehicles under operational conditions involving significant temperature variations represents a key aspect of military-technical science. This paper investigates the complex mechanisms by which thermal oscillations affect metal fatigue processes in high-hardness armor steels, with particular emphasis on welded joints that represent critical sites for crack initiation and propagation. The methodological approach encompassed a systematic analysis of published experimental data from relevant scientific literature, along with the application of fracture mechanics principles and thermomechanical fatigue theory. The results indicate significant temperature sensitivity of fatigue parameters in armor steels, whereby impact toughness at a temperature of -40°C decreases by approximately 47% compared to values at room temperature. The stress intensity factor threshold for the base metal of armor steel class 500 HB is ΔKth = 13.4 MPa·m^(1/2), while the heat-affected zone and weld metal exhibit lower threshold values of 12.6 MPa·m^(1/2) and 10.1 MPa·m^(1/2), respectively. Thermal cycling additionally contributes to damage accumulation through mechanisms that include thermal expansion incompatibility of different microstructural phases, development of residual stresses, and changes in plastic deformation mechanisms. It was concluded that extreme temperature oscillations significantly compromise the integrity of armored structures, and that the design of military vehicles must take into account the synergistic effect of mechanical loading and thermal cycles.