A surgical stapling assembly, comprising: a cartridge jaw, comprising: a proximal end; a distal end positioned opposite said proximal end; a bottom wall; a lateral side wall extending from said bottom wall; and a plurality of jaw windows (3127, 3128, 3129) defined in said lateral side wall; a firing member movable toward said distal end during a firing stroke; and a staple cartridge removably positionable in said cartridge jaw, wherein said staple cartridge comprises: a cartridge body; a plurality of cartridge windows (3117, 3118, 3119) defined in said cartridge body, wherein said cartridge windows are aligned with said jaw windows when said staple cartridge is positioned in said cartridge jaw; staples removably stored in said cartridge body; and a sled movable toward said distal end during said firing stroke to eject said staples from said cartridge body, wherein said sled is visible through the aligned cartridge windows and jaw windows as said sled passes the aligned cartridge windows and jaw windows during said firing stroke such that the progress of said sled during said firing stroke is observable through said cartridge windows and said jaw windows. a cartridge jaw, comprising: a proximal end; a distal end positioned opposite said proximal end; a bottom wall; a lateral side wall extending from said bottom wall; and a plurality of jaw windows (3127, 3128, 3129) defined in said lateral side wall; a proximal end; a distal end positioned opposite said proximal end; a bottom wall; a lateral side wall extending from said bottom wall; and a plurality of jaw windows (3127, 3128, 3129) defined in said lateral side wall; a firing member movable toward said distal end during a firing stroke; and a staple cartridge removably positionable in said cartridge jaw, wherein said staple cartridge comprises: a cartridge body; a plurality of cartridge windows (3117, 3118, 3119) defined in said cartridge body, wherein said cartridge windows are aligned with said jaw windows when said staple cartridge is positioned in said cartridge jaw; staples removably stored in said cartridge body; and a sled movable toward said distal end during said firing stroke to eject said staples from said cartridge body, wherein said sled is visible through the aligned cartridge windows and jaw windows as said sled passes the aligned cartridge windows and jaw windows during said firing stroke such that the progress of said sled during said firing stroke is observable through said cartridge windows and said jaw windows. a cartridge body; a plurality of cartridge windows (3117, 3118, 3119) defined in said cartridge body, wherein said cartridge windows are aligned with said jaw windows when said staple cartridge is positioned in said cartridge jaw; staples removably stored in said cartridge body; and a sled movable toward said distal end during said firing stroke to eject said staples from said cartridge body, wherein said sled is visible through the aligned cartridge windows and jaw windows as said sled passes the aligned cartridge windows and jaw windows during said firing stroke such that the progress of said sled during said firing stroke is observable through said cartridge windows and said jaw windows.