I had to google it...I'm actually thinking of getting another to chuck in the van to replace an old US Army ECWCS level 5 jacket that goes everywhere.
The Extended Cold Weather Clothing System (ECWCS) is a protective clothing system developed in the 1980s by the United States Army Natick Soldier Research, Development and Engineering Center.

For those with itchy credit cards - https://www.military1st.co.uk/10615001-mil-tec-ecwcs-jacket-with-fleece-olive.html