Government agencies face the challenge of selecting and prioritizing research and development (R&D) investments to address security threats in a dynamic threat landscape. This challenge is compounded by the fact that proposed projects often span technology readiness levels (TRL), cost, and developmental timeframes. The following paper describes a probabilistic, risk-based method that assesses the future expected value of potential investments, incorporating uncertainty from the threat environment - both current and projected - and uncertainty in technology development. The developed method facilitates hedging strategies and redirection of investments at future decision points, based on shifts in threat and reduction of uncertainty; it also captures discounting of achieved value over time to balance projects that have a smaller but faster realization of risk reduction with longer-term solutions that have a large reduction. Ultimately, this approach to R&D investments produces clear, quantitative results for a balanced portfolio that maximizes expected risk reduction.