The B-1 secondary power subsystem is described and an overview of interfacing subsystems is given. The systems are designed to provide a high degree of air vehicle self-sufficiency and rapid deployment capability. Systems integration for minimum weight and volume is emphasized.Each of the airframe-mounted accessory drive gearboxes may be shaft-driven by either the related propulsion engine or an auxiliary power unit( APU). Stored hydraulic energy is used for APU starting. The engines are started with APU power transmitted through fill-and-drain torque converters in the accessory drive gearboxes. An acceleration limiting device is employed for coupling the gearbox accessory drive train to the APU. System control is highly automated.Ground test experience to date has shown system functional operation and performance to be in conformance with design expectations. All vehicle flight tests are imminent.