An engineer combat battalion (ECB) was a designation for a battalion-strength combat engineering 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]

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. They also fielded defensive .30 cal. and .50 cal. machine gun squads, anti-tank rocket and grenade launchers, and were required to fight as infantry when needed.^[2]

Combat engineers played important roles in numerous World War II battles, especially breaching the heavily fortified Siegfried Line protecting the German border and numerous defensive lines established by the Wehrmacht in Italy, including the Gustav Line. Among the most familiar for their heroism and contributions to establishing key bridgeheads in the European Theater was at the Ludendorff Bridge at the Battle of Remagen.

Combat engineers also played roles in several unconventional operations, including the securing of elements of the German nuclear weapons program in Operation Big^[3] and recovery of stolen art and treasure subsequently returned to its original owners by the Monuments Men.^[3]

In the Pacific Theater the U S Army 42nd Combat Engineers took part in the hard-fought high casualty Battle of Attu Aleutian Islands (1943) and the Battle of Manila, Luzon Philippines (1945), earning 2 Battle Stars.