As the initial waves of Allied forces broke through the German defenses and pushed inland, thousands more waited to come ashore. These troops would help replace casualties from units that suffered tremendously during the first few waves of the invasion. All told, more than 21,000 American soldiers would land at Utah Beach on June 6, with another 35,000 coming ashore at Omaha. As the beaches were being cleared of obstacles and mines, logistical support units began bringing much-needed supplies and equipment to those pushing ahead inland. Follow-on operations also saw the employment of Mulberry Harbors: portable, temporary breakwaters and piers that enabled the Allies to unload large quantities of supplies until the port cities could be captured and utilized.