The Gyro Horizon Indicator is more commonly referred to as the virtual horizon. It provides the pilot with an estimation of where the horizon is relative to the aircraft. This particular gyro is not dated, however it's construction makes us beleive that it is from the 1940s.
This particular gyro model was used in almost all American aircraft of the war. The advantage of this, being that it is an easily exchangable part, which is important considering how essential it is in flight. While flying at night or in cloud cover, a pilot is easily disoriented, and without this instrument they could easily drift towards the ground or into a stall.