What They Did
Some of the engineers were trained in explosives that were used in demolishing structures such as bridges which might later be used by the enemy. The explosives also were used to remove obstacles placed by the Germans. For the 300th Engineers, demolition was not their primary mission but they were trained in demolition techniques. They used that training and explosives to accomplish many of their missions. In the Battle of the Bulge, the 300th blew up bridges to delay the German advance. In some cases, they built the replacement bridges for bridges they had already blown up.
Another use of explosives was in providing water for troops and civilians. They used explosives to blow a deep hole in a small stream that created a sump and enabled them to pump to the nearby water purification station they had set up. The 300th Engineers also used explosives to blow up defensive obstacles placed by the Germans that included barbed wire entanglements, felled trees, disabled equipment and whatever else the Germans improvised to slow down Allied advances.
Explosives were used to remove the German pillboxes. The 300th enlisted rifle-grenades, bazookas and machine guns chipping away at the gun ports to silence the pillbox defenders. Once the pillbox was not returning fire, the 300th stacked TNT against the steel door of the pillbox and blew it open. Once inside, they detonated any remaining gun power with their explosives so the guns could not be used again.
So crucial is this aspect of engineering that the Basic Field Manual of June, 1943 states specifically that "Demolitions are usually ordered at critical times; and the failure of a single demolition could cost the lives of hundreds of men. YOU MUST NOT FAIL." According to US Army Corps of Engineers historian, Dr. Larry Roberts, engineers used "TNT, Composition C, Composition C-2, and regular dynamite. On occasion, engineer units would use captured enemy explosives... "
Men of the 300th performed a wide range of demolitions according to Randy Hanes, veteran of the 300th:
We used explosives many times: blowing bridges in the Bulge, blowing deep holes in small streams, forming a sump, to pump water for our Water Purification Stations and blowing defensive obstacles put up by the Germans, such as barbed-wire entanglements. Pillboxes were not "removed", we just blew the hell out of them, and we used rifle grenades to chip away at gun ports, also bazookas and machine guns. After silencing the defenders we stacked much TNT at the steel doors [and] blew them open.