From 1919 to 1932 in Britain, the Royal Commission on Awards to Inventors compensated private inventors of valuable WWI technologies. This paper asks what characteristics of invention mattered for the Commission’s judgments on merit. I find that they understood invention as a problem-solving process comprising both theoretical and empirical work –describing the ideal solution using known theorems, building a physical imitation by updating known devices, then iterating the prototype based on user feedback. Meritorious inventors presented either a novel solution or means of implementation; they also supervised iteration through to deployment. While partially similar to existing ideas about “inventor-entrepreneurs”, the Commission’s thought displays original insights into the nature of novelty, science versus technology, and the challenge of inventing for militaries. After reviewing the multi-disciplinary literature on invention, I elaborate the Commission’s philosophy and clarify its key features using three example rulings: dazzle camouflage, TNT manufacture, and fire control systems.