156-inch Solid Rocket Booster Segment

The mock-up of the hardware described in the caption in the adjacent picture. ATK (formerly Morton-Thiokol) outdoor display in northern Utah, USA. This was a major rocket development facility during the Cold War and beyond.
Update: Realizing that the "adjacent photo" no longer contains the interpretive sign, I added that photo in a note.
UPDATE 2: This is actually a mock-up of the motor for the Minuteman first stage. It's obviously not 156 inches in diameter!