Collar disk US Army EM/NCO Engineers WW2

An Engineer Combat Battalion (ECB) was a designation for a battalion-strength combat engineer unit in the U.S. Army, most prevalent during World War II. They are a component of the United States Army Corps of Engineers. Also known as "Combat Engineer Battalions", they were typically divided into four companies: A, B, C, and Headquarters and Service (H&S).[1]: Chapter 5  Best known for pontoon bridge construction and clearing hazards in amphibious landings, their duties also included serving as sappers deploying and deactivating explosive charges and unexploded munitions, mapmaking, camouflage, and a wide variety of construction services supporting frontline troops. With a secondary mission of fighting as infantry when required, they were armed with .30 cal. and .50 cal. machine guns, bazookas and grenade launchers