A surgical instrument comprising: a firing member assembly including a portion supported for selective axial movement in a distal direction and a proximal direction; a drive unit, comprising: a motor including a motor shaft; and a gear assembly drivingly coupled to the motor shaft and including an output shaft assembly configured to apply rotary motions to the firing member assembly such that upon rotation of the motor shaft in a first rotary direction, the portion of the firing member assembly is axially driven in the distal direction and upon rotation of the motor shaft in a second rotary direction, the portion of the firing member assembly is axially driven in the proximal direction; and the surgical instrument further comprising: a retraction assembly interfacing with the firing member assembly for manually applying other rotary motions to the firing member assembly in the second rotary direction when the motor is deactivated; and locking means interfacing with the retraction assembly and the drive unit for preventing the other rotary motions from driving the gear assembly during operation of the retraction assembly while the gear assembly remains drivingly coupled to the motor shaft, the surgical instrument further comprising a housing and the motor including a motor housing, characterised in that the gear assembly includes a gear box housing non-movably coupled to the motor housing, the motor housing and the gear box housing being supported within the housing for rotation relative thereto as a unit upon application of the other rotary motions to the firing member assembly. a firing member assembly including a portion supported for selective axial movement in a distal direction and a proximal direction; a drive unit, comprising: a motor including a motor shaft; and a gear assembly drivingly coupled to the motor shaft and including an output shaft assembly configured to apply rotary motions to the firing member assembly such that upon rotation of the motor shaft in a first rotary direction, the portion of the firing member assembly is axially driven in the distal direction and upon rotation of the motor shaft in a second rotary direction, the portion of the firing member assembly is axially driven in the proximal direction; and a motor including a motor shaft; and a gear assembly drivingly coupled to the motor shaft and including an output shaft assembly configured to apply rotary motions to the firing member assembly such that upon rotation of the motor shaft in a first rotary direction, the portion of the firing member assembly is axially driven in the distal direction and upon rotation of the motor shaft in a second rotary direction, the portion of the firing member assembly is axially driven in the proximal direction; and the surgical instrument further comprising: a retraction assembly interfacing with the firing member assembly for manually applying other rotary motions to the firing member assembly in the second rotary direction when the motor is deactivated; and locking means interfacing with the retraction assembly and the drive unit for preventing the other rotary motions from driving the gear assembly during operation of the retraction assembly while the gear assembly remains drivingly coupled to the motor shaft, the surgical instrument further comprising a housing and the motor including a motor housing, characterised in that the gear assembly includes a gear box housing non-movably coupled to the motor housing, the motor housing and the gear box housing being supported within the housing for rotation relative thereto as a unit upon application of the other rotary motions to the firing member assembly. a retraction assembly interfacing with the firing member assembly for manually applying other rotary motions to the firing member assembly in the second rotary direction when the motor is deactivated; and locking means interfacing with the retraction assembly and the drive unit for preventing the other rotary motions from driving the gear assembly during operation of the retraction assembly while the gear assembly remains drivingly coupled to the motor shaft, the surgical instrument further comprising a housing and the motor including a motor housing, characterised in that the gear assembly includes a gear box housing non-movably coupled to the motor housing, the motor housing and the gear box housing being supported within the housing for rotation relative thereto as a unit upon application of the other rotary motions to the firing member assembly.