Competition, innovation, and cost-containment in the missile defense sector are vital to countering rapidly evolving missile threats from China, Russia, and other sources. History has taught us that excessive consolidation in any industry, especially defense, has increased taxpayers’ costs and high-level clumsiness in strategic thinking. That’s why Washington should prohibit Lockheed Martin’s proposed acquisition of Aerojet Rocketdyne and take other decisive actions to promote enhanced competition in the already highly-concentrated missile defense, propulsion, and hypersonic development market.