A surgical cutting and stapling end effector, comprising: a channel configured to operably support a removable staple cartridge that includes surgical staples stored therein that are ejected from the removable staple cartridge as a sled that is movably supported therein is moved from a starting position to an ending position in the removable staple cartridge; a rotary end effector drive shaft supported within said channel and being selectively rotatable by a source of rotary motion applied thereto; and a firing assembly movable from a first position wherein said firing assembly is longitudinally movable through said channel and a second locked position wherein said firing assembly is prevented from moving distally through said channel, said firing assembly being biased into said first position prior to rotation of said rotary end effector drive shaft and moving to said second position upon rotation of said rotary end effector drive shaft unless a sled of a removable staple cartridge that has been seated in said channel is in the starting position and retainingly engages said firing assembly to thereby retain said firing assembly in said first position during further rotation of said rotary end effector drive shaft, said firing assembly comprising: a firing body movably supported on said rotary end effector drive shaft; a rotary advancement member in driving engagement with said rotary end effector drive shaft and in driving engagement with said firing body, said rotary advancement member being movable between said first and second positions relative to said firing body; and a biasing member between said firing body and said rotary advancement member to bias said rotary advancement member into said first position. a channel configured to operably support a removable staple cartridge that includes surgical staples stored therein that are ejected from the removable staple cartridge as a sled that is movably supported therein is moved from a starting position to an ending position in the removable staple cartridge; a rotary end effector drive shaft supported within said channel and being selectively rotatable by a source of rotary motion applied thereto; and a firing assembly movable from a first position wherein said firing assembly is longitudinally movable through said channel and a second locked position wherein said firing assembly is prevented from moving distally through said channel, said firing assembly being biased into said first position prior to rotation of said rotary end effector drive shaft and moving to said second position upon rotation of said rotary end effector drive shaft unless a sled of a removable staple cartridge that has been seated in said channel is in the starting position and retainingly engages said firing assembly to thereby retain said firing assembly in said first position during further rotation of said rotary end effector drive shaft, said firing assembly comprising: a firing body movably supported on said rotary end effector drive shaft; a rotary advancement member in driving engagement with said rotary end effector drive shaft and in driving engagement with said firing body, said rotary advancement member being movable between said first and second positions relative to said firing body; and a biasing member between said firing body and said rotary advancement member to bias said rotary advancement member into said first position. a firing body movably supported on said rotary end effector drive shaft; a rotary advancement member in driving engagement with said rotary end effector drive shaft and in driving engagement with said firing body, said rotary advancement member being movable between said first and second positions relative to said firing body; and a biasing member between said firing body and said rotary advancement member to bias said rotary advancement member into said first position.