Understanding crack propagation in functional materials is critical to extending the lifetime of materials in aerospace, energy, and transportation. Titanium-6242S is used for demanding applications such as static and rotating gas turbine engine components; some of the most critical and highly-stressed civilian and military airframe parts are made of these alloys. In aerospace turbine engines, near-alpha titanium alloys are often used in high humidity environments, this is important to develop an understanding of subcritical crack growth response when exposed to water vapor. A custom environmental fatigue system was developed to identify the controlling processes for the high cycle fatigue crack growth of Titanium-6242S. The small crack growth behavior, the number of cycles to failure, and crack growth rate were used to calibrate simple models and methods for further environmental crack propagation experiments and analysis. Understanding how air and water pressure play a role in the overall life cycle of Titanium-6242S could save money and secure the safety of passengers on an aircraft.