The M51 Wool uniform
In 1951, the US Army introduced the OG 108 wool/nylon field uniforms during the Korean War to update their cold weather gear. Although it was designed to replace earlier winter uniforms, it didn't become widely used until after the conflict. While the OG 108 was meant to be worn under M1951 trouser shells and jackets, some commanders authorized it as a standalone winter uniform due to its appearance.
The OG 108 uniform was used by the US Army into the early 2000s. You can see it here on two soldiers from the 172nd Infantry Brigade, right after they finished the Air Assault course around 1985-1986. Even though these uniforms are over 70s years old, they're still incredibly durable and perfect for tough outdoor conditions. The wool/nylon blend was designed for warmth and comfort, making them great for all sorts of challenging environments.