This work conducts an exploratory evaluation of the brittle fracture behavior for an ultrahigh strength martensitic steel using conventional three-point bend SE(B) and precracked Charpy V-notch (PCVN) specimens. A primary purpose of this study is to verify the effectiveness of the Master Curve methodology in providing a reliable estimate of the reference temperature (T₀) derived from fracture toughness data sets measured in the ductile-to-brittle transition (DBT) region of an ultrahigh strength, low alloy martensitic steel. Fracture toughness testing conducted on three-point bend SE(B) specimens and PCVN configurations at different test temperatures in the DBT region provides the cleavage fracture resistance data in terms of the J-integral at cleavage instability, J_c, and its corresponding K_Jc-values for the tested material. Although this class of ultrahigh strength steel having a martensitic microstructure is currently beyond the reach of ASTM E1921, Standard Test Method for Determination of Reference Temperature, T0, for Ferritic Steels in the Transition Range, the analyses described here show that the predicted normalized curves of median fracture toughness versus temperature are in good agreement with the experimental measurements.