This is an excerpt - the whole article is here.
To clear the beach, the invasion planners envisioned an aerial and naval bombardment sweeping the coastline. Then the initial wave of infantry, supported by specially designed amphibious tanks, would land at low tide after dawn and rush up to secure the beaches.
Following in their wake, the NCDUs would land with a mission to blow a 50-yard gap in the German obstacles, and place markers so landing craft coming in later that morning at high tide would have a straight, unobstructed path leading to the beach.
For the Americans, the hypothetical beaches were "Utah" and "Omaha." At 0630, H-Hour, on the morning of June 6, 1944, 11 NCDUs came in with the 8th Infantry Regiment at Utah. With the Army securing the beach, the Navy demolition men went to work and quickly blew eight 50-yard gaps and had enough time to expand one gap to 700 yards. This allowed follow-on waves of troops to pour ashore and quickly secure a substantial beachhead by midday.
Four sailors were killed during the mission and 11 others were wounded. Because of their efficient work, these units received a Navy Unit Commendation.
At Omaha, the Germans were better entrenched and had built a more robust network of obstacles. It didn't bode well for the 16 incoming NCDUs that the pre-invasion air and sea bombardments mostly missed their marks. Also, choppy seas swamped many of the amphibious tanks, depriving the invaders of needed close-in firepower.
As a result, the invaders were savaged by heavy artillery, mortar and machine gun fire that ripped into the NCDU landing craft and followed the brave sailors as they struggled to demolish the obstacles.
Hostile action accounted for 31 killed and 60 wounded, a casualty rate of more than 50 percent. Yet by the time of the first high tide, the units had created five gaps for follow-on waves to use to get to the tenuous beachhead. When the tide receded that afternoon, the surviving demolition experts plunged back into the surf to create seven more gaps, some as wide as 150 yards.
Through those gaps poured the reinforcements needed to hold off any counterattacks and take the fight inland. Seven sailors earned the Navy Cross for their work that day.
For their heroic actions, the Omaha NCDUs received a Presidential Unit Citation.
