Wind turbine drivetrains consist of components that directly convert kinetic energy from the wind to electrical energy. Therefore, guaranteeing robust and reliable drivetrain designs is important to prevent turbine downtime. Current drivetrain models often lack the ability to model both the impacts of electrical transients as well as wind turbulence and shear in one package. In this paper, the capability of the FAST wind turbine computer-aided-engineering tool, developed by the National Renewable Energy Laboratory, is enhanced through the integration of a dynamic model of the drivetrain. The dynamic drivetrain model is built using Simscape in the MATLAB/Simulink environment and incorporates detailed electrical generator models. This model can be used to evaluate internal drivetrain loads due to excitations from both the wind and generator.