The Pro-Neck-Tor (PNT) helmet was developed to reduce the incidence of cervical spine injuries during head-first impacts. It consists of an inner- and outer-shell that are connected by an internal guide mechanism. In an impact the mechanism deploys and guides the inner shell and head relative to the outer shell, such that the neck moves into flexion or extension. The deployment mechanism is intended to induce flexion in impacts slightly posterior to the vertex of the head, and extension in slightly anterior impacts. The purpose of this work was to develop a multibody dynamics model of the Hybrid III head and PNT helmet that can be validated experimentally, and allows us to assess the functionality of the deployment mechanism. The model simulates a drop tower that was configured to validate the model. Five experimental drops were conducted with the impact surface oriented at three different angles (0⁰,15⁰ and -15⁰), and helmet kinematics were measured using high speed video analysis. The model showed good agreement with experimental kinematic corridors. Agreement was strongest for the perpendicular (0⁰), and anterior-to-vertex (15⁰) impact conditions. The quantitative agreement for the posterior-to-vertex (-15⁰) impact condition was not as strong; however the mechanism deployed in the same manner in the experimental and virtual drops in all impact conditions. The deployment mechanism was able to select an appropriate deployment mode in various impact scenarios. Flexion was induced in posterior impacts, and extension was induced in axial and anterior impacts. According to the model, the deployment direction is governed by the moment that results from the forces at the deployment pins and the occipital condyles. This supports our current understanding of the deployment mechanism. The performance of the model is adequate to warrant its use in the continued development of the Pro-Neck-Tor helmet.