A surgical instrument comprising: an end effector; a firing member; a trigger; a firing drive (170, 172) configured to selectively advance the firing member relative to the end effector; a reversing drive (496, 406, 401, 403, 416, 798) configured to selectively retract the firing member, wherein the firing drive (170, 172) is configured to advance the firing member upon an actuation of the trigger and the reversing drive (496, 406, 401, 403, 416, 798) is configured to retract the firing member upon a subsequent actuation of the trigger; the firing drive including a pawl selectively engageable with the firing member in order to advance the firing member wherein the pawl can be disengaged from the firing member when the reversing drive (496, 406, 401, 403, 416, 798) is engaged with the firing member; the reversing drive including a gear train (496, 406, 401, 403, 416) and a return pin, the gear train (496, 406, 401, 403, 416) having a first gear operably engaged with the firing member and a second gear operably engaged with the trigger, wherein the second gear is selectively operable with the first gear via the return pin such that an actuation of the trigger can retract the firing member via the first and second gears (401, 496); and an anti-backup mechanism configured to permit the return pin to rotate in a first direction yet prohibit the return pin from rotating in a second direction opposite the first direction when the firing member is advanced, including an indexing mechanism (711, 811, 911), wherein the indexing mechanism (711, 811, 911) comprises a plurality of recesses or apertures (713a-d), each of which is configured to sequentially hold the return pin after the return pin rotates in the first direction upon a respective actuation of the trigger that advances the firing member. an end effector; a firing member; a trigger; a firing drive (170, 172) configured to selectively advance the firing member relative to the end effector; a reversing drive (496, 406, 401, 403, 416, 798) configured to selectively retract the firing member, wherein the firing drive (170, 172) is configured to advance the firing member upon an actuation of the trigger and the reversing drive (496, 406, 401, 403, 416, 798) is configured to retract the firing member upon a subsequent actuation of the trigger; the firing drive including a pawl selectively engageable with the firing member in order to advance the firing member wherein the pawl can be disengaged from the firing member when the reversing drive (496, 406, 401, 403, 416, 798) is engaged with the firing member; the reversing drive including a gear train (496, 406, 401, 403, 416) and a return pin, the gear train (496, 406, 401, 403, 416) having a first gear operably engaged with the firing member and a second gear operably engaged with the trigger, wherein the second gear is selectively operable with the first gear via the return pin such that an actuation of the trigger can retract the firing member via the first and second gears (401, 496); and an anti-backup mechanism configured to permit the return pin to rotate in a first direction yet prohibit the return pin from rotating in a second direction opposite the first direction when the firing member is advanced, including an indexing mechanism (711, 811, 911), wherein the indexing mechanism (711, 811, 911) comprises a plurality of recesses or apertures (713a-d), each of which is configured to sequentially hold the return pin after the return pin rotates in the first direction upon a respective actuation of the trigger that advances the firing member.