Aircraft carriers allow navies to move air power across oceans without relying on nearby air bases. China developed the DF-21D missile to threaten the ships that make those operations possible.Known as a “carrier killer,” the DF-21D is a land-based anti-ship ballistic missile designed to strike large warships at sea. Its reputation comes from a combination of long range, a maneuverable reentry vehicle, and the challenge it presents to carrier defenses.The nickname, however, describes its intended mission. Whether it can successfully strike a moving carrier in wartime depends on much more than the missile itself.A ballistic missile built to attack shipsThe DF-21D belongs to China’s Dong Feng, or “East Wind,” missile family. Unlike variants intended to attack targets on land, it carries a conventional warhead for strikes against ships, including aircraft carriers.According to the Congressional Research Service, the missile has a range exceeding 1,500 kilometers (roughly 932 miles). That gives China a way to threaten naval vessels far from its coastline using land-based launchers.The distinction from an anti-ship cruise missile is important. Cruise missiles typically use powered flight within the atmosphere. A ballistic missile follows a high, arcing trajectory before its reentry vehicle descends toward the target.For naval planners, this introduces another direction and type of attack to defend against. CRS notes that before these weapons emerged, the US Navy had not faced highly accurate ballistic missiles capable of hitting moving ships at sea.A warhead that can adjust its approachRange alone cannot explain the “carrier killer” label. An aircraft carrier can change course and speed, making its position at launch different from its location when a missile arrives.The Pentagon’s 2024 China Military Power Report identifies a maneuverable reentry vehicle as a feature of the DF-21D. This vehicle carries the warhead back through the atmosphere and can adjust its flight path during the approach.That maneuverability supports the missile’s anti-ship role, although publicly available information does not establish its accuracy against a defended carrier under combat conditions.The DF-21D also operates from road-mobile launchers. These vehicles can relocate, making them harder to find and target than fixed launch sites. Mobility adds another complication for forces attempting to eliminate the threat before launch.Together, these features explain why the missile attracts attention: it combines a long-distance strike capability with a system intended to engage ships that do not remain stationary.Why sinking a carrier remains a difficult taskA missile cannot attack a carrier effectively without reliable targeting information. China must first detect the ship, identify it, determine its position, and maintain sufficient tracking information to support the strike.That information must reach the launch unit, and the reentry vehicle must then find the intended ship. This sequence is commonly called the targeting “kill chain.” Failure at any stage can undermine the attack.Carrier groups also have defensive options. CRS discusses missile interceptors, electronic warfare, deception, and measures that obscure a ship’s location as ways to challenge anti-ship ballistic missiles.None guarantees protection, but their existence means the DF-21D’s range cannot be treated as an automatic no-go zone.The missile’s significance lies in the risk it introduces. A credible threat to a carrier can complicate decisions about positioning, protection, and how its aircraft conduct operations.That is why the “carrier killer” name has endured. The DF-21D was built to challenge a central instrument of American naval power, but its intended capability should not be confused with a guaranteed wartime outcome.