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Some results of the supersonic transport materials research conducted by Douglas-McDonnell in the areas of fracture toughness, and by Douglas in the area of crack propagation, are presented. The results of tests on centrally notched fracture toughness specimens of steels, titaniums, and superalloys are described. The crack propagation studies show results of testing cracked specimens under uniaxial and biaxial states of stress at room and elevated temperatures, and the extent of material deterioration in stiffened panels. Methods of analyses for crack propagation and residual crack strength are presented and comparisons are made between analysis and test.