Gun Sight, Ball Turret, Type K-4 Sperry, B-17, B-24

This is an electro-mechanical, automatic Type K-4 Computing Gun Sight used in the Sperry ball turret in WWII-era heavy bombers such as the B-17 Flying Fortress and B-24 Liberator. 

Mounted within the ball turret, it hung from the 'ceiling' of the turret just in front of the forehead of the turret gunner (see illustration from turret manual). The gunner took aim at his target by looking through the glass screen mounted on an optic head the bottom of the sight, which is aligned to peer through the circular window between his feet.  The gunner has set the target length and range on the sight using the knobs shown, which projects three lines called reticles (1 horizontal and 2 vertical), and informs the computer of the targets direction by rotating the turret. The computing sight automatically calculates the deflection, adjusts the projection of the reticles on the glass screen toward the target.  Then the gunner may greet the uninvited guest with 50 cal potpourri.

The photos show both the external and internal workings of the gun sight: an exquisite electro-mechanical computer developed well before the era of microchips.