The U.S. Army envisions a fully developed Augmented Reality (AR) system to provide the Warfighter with an exceptionally realistic training experience. The real time blending of virtual objects into the live training environment would permit the Warfighter to train with and against virtual 3D objects, displaying realistic behavior. The key interface into a live AR environment is the Head Mounted Display (HMD). Currently most off-the-shelf HMDs are either the "fully occluded" type (used for virtual reality applications) or the "video see through" type (used for mixed reality applications). While widely available from industry at reasonable costs, these types of HMDs are limited by restricted fields-of-view and have significant video latency, both are major hindrances. Neither is suited for the live training environment. On the other hand, an "Optical See-Through-" type of HMD (OST-HMD) would permit one to directly view the live environment through a transparent lens—using natural vision and a normal field-of-view—as opposed to viewing occluded video playback directly from HMD mounted cameras. Therefore, OST-HMDs should be much better suited to support unrestricted movement throughout a live physical training environment. Currently, when OST-HMDs are used in the live environment, the virtual images produced are see-through and "ghostly", thus their appearance is unrealistic. There is a need to increase the capability of OST-HMDs in order to produce 3D virtual imagery of sufficient opaqueness and contrast resolution where viewers believe the virtual objects are a natural part of the live environment. In order to address this technology gap, the U.S. Army Research Laboratory, Human Research and Engineering Directorate, Simulation and Training Technology Center (ARL-HRED-STTC) and Trex Enterprises Corporation are conducting research into improving the quality of OST-HMDs for live training applications. This paper will review requirements as well as the most recent results of ongoing research in this technology area.