Another little-known role for the B-58A was that of flying testbed for the General Electric J93 turbojet
The General Electric J93 turbojet engine was designed as the powerplant for both the North American XB-70A Valkyrie bomber and the North American XF-108 Rapier interceptor. The J93 was a single-shaft axial-flow turbojet with a variable-stator compressor and a fully-variable convergent/divergent exhaust nozzle. The maximum sea-level thrust was 31,500 pounds.
The J93 engine was ready before either the XB-70A or the XF-108 were, so the Air Force concluded that the engine should be initially flight tested in an existing aircraft. B-58A serial number 55-662 was selected for the project, and on July 1, 1959, Convair began the modification of the aircraft so that it could accept the installation of a J93 engine in a specially-modified underfuselage pod. Following the completion of the Convair modifications, the aircraft was delivered to General Electric's Edwards AFB operation as a NB-58A. While there, a J93-GE-3 engine was installed in a special underfuselage pod.
Unfortunately, the F-108 interceptor was cancelled outright and the B-70 project was reoriented
to a research project only. A few NB-58A ground runs were made with the J93 engine in place, but the day before
the first flight was scheduled to take place, the funding for the NB-58A project was cancelled.
Consequently, the NB-58A/J93 combination never took to the air. The special pod was removed
from the NB-58 testbed, and the NB-58A itself was converted to a TB-58A and later flew chase
missions for the XB-70A at Edwards AFB. It was consigned to storage at MASDC in 1970, and
eventually scrapped in 1977.