Advances in drone technology and artificial intelligence seem destined to transform defense planning and budgeting. But we shouldn’t assume these innovations will render obsolete manned weapons systems. It would be a strategic and costly mistake to cut the procurement of existing programs that we need in the short term. Given the real chance of great power conflict in the near future—well before new technologies now in the research and development phase are ready to use—the United States must continue fielding traditional combat-relevant systems and weapons while continuing to research and develop the next generation of defense technologies. This isn’t a...