Northrop Grumman has officially reached the low-rate production stage of its $5 billion B-21 Raider program. Today, two have been delivered to the US Air Force for operational testing and validation before they are officially introduced to active service at Ellsworth Air Force Base (RCA) next year. The USAF is slated to receive at least 100 of the sixth-generation stealth bombers to fulfill the dual role of nuclear deterrence and conventional strategic strike, but is already considering expanding to 145 or more. The B-21 is more than just a successor to the B-2 Spirit, but rather a radical breakthrough in…