This paper details the development of an abdominal injury assessment device for loading due to belt restraint submarining in the Hybrid III family of dummies. The design concept and criteria, response criteria, choice of injury criterion, and validation are explained. Conclusions of this work are: 1) Abdominal injury assessment for belt loading due to submarining is now possible in the Hybrid III family of dummies. 2) The abdomen developed has biofidelity in its force deflection characteristics for belt loading, is capable of detecting the occurrence of submarining, and can be used to determine the probability of abdominal injury when submarining occurs. 3) Installation of the abdomen in the Hybrid III dummy does not change the dummy kinematics when submarining does not occur. 4) When submarining does occur, the dummy kinematics are very similar to baseline Hybrid III kinematics, except for torso angle. The change in torso angle is or may be a result of a more human-like compliance in the abdomen.