Two relevant materials found in ground vehicle underbody armor/hull designs are Aluminum 2139-T8 and RHA Steel (Class I). These are 2 very important materials that need a thorough understanding of their high-strain rate behavior. The Johnson-Cook Deformation (JC-D) model at this time is the most preferred constitutive material model to utilize for high-strain (large deformation) blast simulations. The JC-D Model contains five empirically-based input parameters which can be determined traditionally through a series of uniaxial laboratory tests where each target parameter is isolated, while the remaining parameters are held constant. There are many criticisms and problems with this approach. The objective of this two part paper is to present and adopt a more accurate approach with less criticism to the determination of these five input parameters through both a sensitivity study to determine which input parameters are the most sensitive to a particular chosen response which in return will be utilized to conduct a numerical / empirical physics-based approach known as Numerical Optimization. Part 1 will focus on the sensitivity study while part 2 will focus on the optimization study and validations to determine optimal values for the JC-D Material Model Input Parameters. In part2, these optimized material input parameters will be leveraged to run shock tube simulations after which validations with various shock-tube blast load tests under various geometrical and or loading conditions such as plate thickness, pressure loading, boundary conditions, etc. will be made.