Since at least 1997, work has been ongoing to address the human behavior representation (HBR) gap in military simulations (Hutson, 1997; Cornwell et al., 2003; Silverman et al., 2006). In 2018, the Army formally recognized the HBR gap, initializing an effort to reduce it. Prior to that, the RAND Corporation was commissioned by the US Army to develop a method to analyze and account for the will to fight of partner nations in support of operations. Two RAND reports (2018a, 2018b) describe the development of a model and method of analyzing the construct of will within a military context. The Will to Fight model has evolved from a report to a software instantiation using a game environment as well as a constructive simulation. This paper and presentation will describe the development of the Will to Fight model and the instantiation of the game as well as our progress on the development of a referent software implementation of the model to be experimented on by the Army with the goal of incorporation into the OneSAF program of record. As of January 2019, the modeling and initial coding preparations are underway. Implementation and initial testing in the IWARS simulation and OneSAF will be conducted throughout 2019. Assessment of the process will be iterative with observation and participation of AMSO, PEO-STRI, and other U.S. Army stakeholders including the Soldier Lethality, Synthetic Training Environment, and Army Position, Navigation & Timing, Cross-Functional Teams of Army Futures Command. The current one-year effort will conclude in January 2020 with a working Will to Fight agent- and unit-level model suitable for full testing and iterative improvement and modification in official U.S. Army simulations. RAND will transfer control of the Will to Fight model to the U.S. Army in 2020 according to the OneSAF user agreement.