Behind armour blunt trauma (BABT) has been investigated in depth for anterior impacts, but there are only a few studies regarding posterior BABT. The objective of this study is the numerical analysis of posterior BABT and the comparison to anterior BABT using the GHBMC M50-P. Two posterior impacts (vertebra T7 and between 9th and 10th rib) are compared to two anterior impacts (mid-sternum and 5th rib) by evaluating the body wall deformations and the strains in hard tissues, such as ribs, vertebrae and sternum. Using a substitute impact layer (SIL) to imprint the back face deformation (BFD) and adapting each impact profile individually, it was possible to investigate these impact positions with an equal energy input. Depending on the impacted position, the imprinting of BFD with the SIL-method results in different magnitudes of body wall displacements, with different internal structures being subjected to varying levels of stress. The anterior impacts result in critical strain values in sternum, costal cartilage and ribs, while the posterior impacts result in critical values in ribs and vertebrae. The comparison of both posterior positions with their respective anterior positions reveals higher rib strains in both posterior cases.