Abstract: A high specific modulus shaft for use in a dynamic assembly such as a gas turbine engine is constructed having a metal outer tubular shaft to transmit the torque and an interior shaft constructed of a metal and high modulus filament composite material bonded to the inner diameter of the outer shaft. The outer shaft may be constructed of steel or titanium or superalloy such as Inconel 718. The inner shaft may be constructed of an aluminum matrix in which multiple boron filaments are embedded in axial alignment or of a titanium matrix in which boron filaments coated with silicon carbide or boron carbide are similarly embedded.