Prevailing wisdom suggests that innovation dramatically enhances the effectiveness of a state's armed forces. But self-defeating innovation is more likely to occur when a military service's growing security commitments outstrip shrinking resources. This wide commitment-resource gap pressures the service to make desperate gambles on new capabilities to meet overly ambitious goals while cannibalizing traditional capabilities before beliefs about the effectiveness of new ones are justified. Doing so increases the chances that when wartime comes, the service will discover that the new capability cannot alone accomplish assigned missions, and that neglecting traditional capabilities produces vulnerabilities that the enemy can exploit. To probe this argument's causal logic, a case study examines British armor innovation in the interwar period and its impact on the British Army's poor performance in the North African campaign during World War II. The findings suggest that placing big bets on new capabilities comes with significant risks because what is lost in an innovation process may be as important as what is created. The perils of innovation deserve attention, not just its promises.