A surgical end effector including an elongate channel configured to operably support a staple cartridge therein and a firing element configured to move within the elongate channel between a starting and an ending position. Various arrangements include openings through the bottom of the elongate channel to permit viewing of the firing element as it moves between the starting and ending positions. An anvil may be supported for movable travel relative to the elongate channel and include a plurality of openings therethrough to permit viewing of the cutting element as it moves between the starting and ending positions. Various arrangements include a firing bar attached to the firing element that serves to move the firing element between the starting and ending position. The firing bar may be movably supported with a hollow shaft that has a plurality of openings therethrough for monitoring the position of the firing bar.