The United States' newest stealth bomber, Northrop Grumman Corp.’s B-21 Raider, conducted its first test flight, a key milestone in the $203 billion program that’s meant to stay well ahead of China’s technological advances.

The new phase "is a critical step in the test campaign to provide survivable, long-range, penetrating strike capabilities to deter aggression and strategic attacks,” according to an Air Force statement. Flight testing includes ground testing, taxiing and flying operations.

The distinctive batwing-shaped B-21 is on track for delivery to Ellsworth Air Force Base in South Dakota in the mid-2020s, the service said. Six test aircraft are being made now on the same production line that will be used for combat-ready aircraft — a process praised by lawmakers and the Government Accountability Office because it improves manufacturing and cuts down on costly retrofits.