This work aims to develop and assess a dual-purpose ankle exoskeleton to reduce metabolic costs during walking, based on a product development process, resulting in the development of a quasi-passive exoskeleton prototype. The study started with the development of an entirely passive prototype, comprising a custom-developed exoskeleton structure designed for military purposes. A qualitative and quantitative analysis of this prototype was performed by 30 subjects belonging to the Portuguese Armed Forces. Results show that 17 of the 30 subjects were able to reduce the metabolic costs during walking, with good comfort and range of motion outcomes. However, the clutch system was unable to adapt to each user’s gait pattern. Such outcomes were integrated into a second prototype, leading to the development of a quasi-passive system. Preliminary results show that the system can actuate the ankle according to each user’s gait pattern. Comfort and range of motion also show encouraging results.