This presentation describes Fe-Cr-Ni-W-C-N-V high strength steels designed and fabricated for enhanced damage tolerance and environmental durability. Material designs and characteristics are described by Thermo-Calc software. The design objectives are high strength, low alloy martensitic steels with a short range order structure scale, by nitrogen alloying, specifically to better resist dynamic high pressure loading effects of early onset of failures possible by thermodynamic instabilities, softening of plastic flow, plastic flow instabilities, e.g. shear bands, or decohesion or shear failure along grain boundaries or precipitates. Thermo-Calc phase versus temperature property diagrams at ambient or elevated pressures reveal hardening and toughening phases of low enthalpy, high strength, and thermodynamic stability relative to the matrix at elevated temperature and/or pressure. At elevated pressures there is an absence of microstructure reversion to austenite that may promote softening. At hardening temperatures, there is an absence of phases which may contribute weak or coarse constituent carbides.