This is a very rare item. It's part of the bombing navigation and control system for the B-36 peacekeeper bomber.
I can find references to the A-1A, but little detail. Here's one reference:
The bombing-navigation system incorporating the Y-3 periscope and the A-1A computer, dubbed the K-3A, came to be the standard system for B-36 aircraft and early production model B-52's.
During later modernization programs, the K-1 system was replaced by the much more reliable K-3A system. This included the Farrand Y-3 periscope bombsight, an A-1A improved bombing/navigation computer, and an improved version of the Western Electric AN/APS-23 radar. The Sperry A-1A bombing computer could be used between altitudes of 4700 and 50,000 feet, at grounds speeds between zero and 760 knots.
Note that the Y-3 periscope sight is closely related to the Y-4 periscope sight that we have.