Additive manufacturing and generative design engineering advances that have changed product development for a variety of industries including the aerospace sector. The presentation will explore the accelerated development of the primary structure for a liquid oxygen/methane (LOX/LCH4) rocket engine using a combined generative design and additive manufacturing approach. First, generative design and topological optimization methods were used to rapidly design an optimal structure; then additive manufacturing was employed to develop an investment casting pattern; finally, an aluminum test article was fabricated by investment casting. Using additive technology combined with metal casting, the authors were able to create 3D printed investment casting patterns, encapsulate in refractory shells, and cast within days of design finalization, even with the geometrically complex and organic designs that are produced through generative design. This approach produced an optimal flight hardware prototype in total design cycle of less than three months.