Top Photo: Coast Guard-manned USS LST-21 unloads British Army tanks and trucks onto a Rhino barge during the early hours of the invasion, 6 June 1944. Photograph from the U.S. Coast Guard Collection in the U.S. National Archives.

The scale and scope of Operation Overlord was unprecedented. The numbers of men, vehicles, and supplies coming across the shore in the first few months of the assault are staggering, but what is more impressive is that much of this movement was done over the shore without use of a fixed port. Within 48 hours of the amphibious assault, over 130,000 GIs and some 17,000 vehicles came ashore. With more troops and equipment arriving daily, the amount of supplies required to support this force grew exponentially. By D+4, the force required 6,000 tons of supplies per day, 9,000 by D+10, and over 12,000 by D+16. Over the next two months, the number of troops ashore grew to 1.2 million Americans, along with a quarter-million vehicles and over 5 million tons of supplies and equipment. 

At the strategic and operational levels of war, throughput of men and material into a theater of war are key for success. Movement of divisions, corps, and even whole armies is a logistically intensive endeavor, requiring deliberate planning and skillful execution. Such operations usually require an established deep-water port with gantry cranes, numerous berthing spaces, quays, large staging areas, and a connection to a fairly robust transportation network. For military strategists, securing such locations and capabilities are key objectives in any campaign. 

Harbor facilities were key objectives for the November 1942 Operation Torch landings in North Africa. All three US landings focused on securing ports for the introduction of men, materials, and vehicles. However, starting with Operation Husky in Sicily in July 1943, the Americans developed a new concept in modern expeditionary operations. 

As the US Seventh Army landed at the towns of Licata, Gela, and Scoglitti, none of these locations had a robust port facility capable of supporting large military organizations. The American part of the Sicily invasion initially involved three divisions supported solely by sea-based platforms. In a new application of power projection, US forces provided logistical support over an unprepared beach with little infrastructure. To accomplish this task, the US Army and Navy began using a host of new vessels to build combat power ashore, the Landing Ship Tank (LST), Landing Craft Tank (LCT), and the DUKW (pronounced “duck”) amphibious truck. These three platforms were employed in large numbers providing “logistics over the shore” during the Sicily Campaign.

Landing ships putting cargo ashore on one of the invasion beaches, at low tide during the first days of the operation, June 1944. Photograph from the U.S. Coast Guard Collection in the U.S. National Archives.

Of these three vessels, the LST was of primary importance and a key component of this new method of supply. The basic US design was first floated in October 1942 with initial use in during the Torch invasion. Displacing some 4,000 tons, the craft could carry approximately 100 troops, 16 to 19 tons of equipment, and six to nine landing craft with a range of over 9,000 miles. The largest beaching vessel of the war, the LST could come ashore, ground itself on the shoreline, and then open its hull’s clamshell doors to discharge tanks or vehicles off a bow ramp. Drafting only eight to 14 feet, the vessel was slow and traveled at just 10 knots. Despite being derisively referred to by its crews as a “Large Slow Target,” these ships were worth their weight in gold, and the number available was a key planning consideration for every US amphibious assault of the war.

Assisting in the delivery of men and equipment from ship-to-shore was the LCT. This vessel was the largest open-deck amphibious craft and included a bow-ramp for easy debarkation of wheeled or tracked vehicles. Displacing some 300 tons, it could carry 150 tons of cargo at a top speed of eight to 10 knots. With over 2,000 built, LCTs were often placed in initial assault waves carrying tanks or self-propelled artillery. An inherently flexible design, these vessels were also used as fire support platforms, utility craft, minesweepers, and in salvage operations.

LCT 525 unloads at the the pontoon causeway at “Omaha” beach, forming part of the U.S. Mulberry the man-made harbor off coast of France, built to protect landing craft from storms in English Channel. Official U.S. Navy photograph, now in the collections of the National Archives. 

Perhaps the most flexible platform was the 2.5-ton amphibious truck referred to as the DUKW. This army design included a six-wheeled truck chassis contained within a hull shaped body that included a propeller screw and a rudder. The vehicle could swim with 5,000 pounds of cargo at a speed of five knots. However, once ashore, the DUKW could easily travel inland at speeds up to 45 miles per hour.  The design was often employed bringing smaller artillery pieces and ammunition to shore and in support of retail distribution operations. 

Navy Beach Battalion takes over a German bunker and slit trenches on a Normandy beach, June 11, 1944. Note the LCT and other landing vessels in the background, DUKW amphibious trucks, and barbed wire atop the seawall. Photographed by Combat Photo Unit Eight (CPU-8). Official U.S. Navy Photograph, now in the collections of the National Archives.

For the Overlord invasion, Allied planners envisioned using the large, robust seaport at Cherbourg at the tip of France’s Cotentin Peninsula. Capable of supporting between 26 and 30 divisions, the harbor was a key objective following the initial amphibious assault, with a planned liberation date of D+14. However, the city and its port were not secured until the end of June, on D+24. Even with its capture, retreating German troops destroyed much of the harbor’s infrastructure, damaging the quays, demolishing the cranes, blocking the port entrance with sunken vessels, cratering the breakwater, and destroying the electrical control and heating plants. The Germans did such a thorough job of spiking the harbor that the American engineer charged with its rehabilitation reported that “the demolition of the port of Cherbourg is a masterful job, beyond a doubt the most complete, intensive, and best-planned demolition in history.” The German officer responsible, Admiral Walker Hennecke, was awarded the Knights Cross for his efforts. As a result, this important link in the Allied offensive remained unusable until at least mid-August.

However, Overlord planners at the Supreme Headquarters Allied Expeditionary Force (SHAEF) foresaw the requirement for an interim capability until Cherbourg was fully operational. At the 1943 Quebec Conference, British Commodore John Hughes-Hallet recognized the need: “If we can’t capture a port, we must take one with us.” With backing from British Prime Minister Winston Churchill, the Allies developed artificial harbors that included piers, causeways, and break waters. Known as “Mulberries,” these manmade harbors included a host of breakwaters with colorful names such as “bombards,” “corncobs,” “phoenixes,” and “gooseberries.” Inside the harbors were the British-designed “Lobnitz Piers,” which served as sea-based berths for naval vessels. These piers could offload deep-draft vessels as well as littoral craft such as LSTs and LCTs. Accompanying the piers were “whale” road sections that created a causeway to the shore. With this design, wheeled vehicles could “roll on” and “roll off” of transports, cutting down debarkation times. 

While the Americans remained skeptical of the effort, construction of Mulberries began as early as D+3. Two were planned, with Mulberry A located in the US sector at Omaha Beach and Mulberry B at Arromanches at Gold Beach in the British sector. Once built, Mulberry offloading operations began on June 16. Initial operations were promising as offload times dwindled from previous over-the-shore methods employed by the Americans during operations in the Mediterranean. Unload times for LSTs and larger vessels dropped from 12 hours to less than two. Furthermore, larger amphibious craft did not have to wait for the tide to come in for a beached vessel to leave the beach for another mission. 

U.S. Army vehicles proceeding ashore on a floating causeway of Mulberry A, off Omaha Beach, 16 June 1944. This structure was erected by U.S. Navy SeaBees. Other causeways are being prepared nearby. Photograph from the Army Signal Corps Collection in the U.S. National Archives.

Before the Mulberries were in place, Allied forces were already operating in a deficit. The planned figures for men and equipment moving ashore fell short of expectations. The original Overlord plan called for the landing of over 22,000 troops that first week, but in the next seven days, only 17,000 arrived. Similarly, of the 12,000 tons of supplies requested, only 9,000 came ashore. The same applied to vehicles, with only 2,600 arriving out of the 4,000 scheduled. By June 18, total discharge rates stood at about 72 percent of the planned requirement. Combat power was only slowly developing.  

To make matters worse for the Allies, on June 19–21 a severe storm battered the man-made structures. While Mulberry B was installed in a protective cove within the British sector and remained mostly intact, its American counterpart did not fare nearly as well. Mulberry A’s bombards were torn from their moorings along with its phoenixes, causing waves to bash the pierheads and eventually separate from their whale causeways.  Additionally, smaller vessels and other parts of the structure were also tossed about with the entire synthetic harbor irreparable. Declared unrecoverable, parts from the American structure were then cannibalized for repair on the remaining Mulberry. 

Wrecked pontoon causeway of one of the Mulberry artificial harbors, following the storm of 19-22 June 1944. Photograph credited to SHAEF-OSS. It was taken on 23 June 1944. Official U.S. Navy Photograph, now in the collections of the National Archives.

Given the storm’s fury, the speed of the landing throughput was reduced by 60 percent. With the loss of the American Mulberry and unavailability of Cherbourg, US forces had to rely on the previously proven over-the-shore methodologies. After the storm, 1,500 soldiers were dispatched to clear Omaha Beach to resume offload operations as soon as possible. Every available LST, LCT, and DUKW was pulled into this effort, clearing out landing craft, rhino ferries, pontoons, and other wrecked equipment. With the storms passing, the US logistics effort resumed fully on June 23. However, much to the logisticians’ surprise, both American landing beaches surpassed their previous discharge rates, with Utah moving 6,400 tons and Omaha 10,000 tons. Just over a week after the storm, both beaches handled over 161,000 tons of supplies, and by end of the month, totals reached 298,827 tons. Prior to the storm on D+12, the combined discharge rate at the two beaches was approximately 14,600 tons. After the storm and during the last week of June, Omaha processed 13,500 tons per day, 115 percent of its planned tonnage capacity, and Utah averaged 7,000tons per day, or 124 percent of planned capacity.   

By June 30, 452,460 troops had come ashore instead of the planned 578,971. However, despite this shortfall, 78 percent of envsioned troop movements made it ashore, along with 80 percent of supplies and 65 percent of equipment. While the discharge rates of both beaches never fully met the planned requirement, enough supplies and equipment passed over the beaches to continue the fight inland. The offload rates on Utah and Omaha beaches surpassed those even at Arromaches, where the remaining Mulberry continued to operate.

Tonnage moved ashore during the first month of the Normandy Campaign.

Operation Overlord was indeed an Allied effort to leverage the men, machines, and capabilities of the United Nations. Sustaining the beachhead and enabling subsequent operations ashore required a robust logistics effort both ashore and afloat. However, the complex plans of using a manmade harbor in the American sector were dashed by Mother Nature. Combined with a stubborn German defense of Cherbourg and an efficient spiking of the seaport, building the First US Army’s combat power ashore was much more difficult than anticipated. However, American formations could rely on the proven logistics over-the-shore methods that were developed during previous amphibious assaults. While this method fell short of the envisioned requirement, it provided enough men, material, and equipment to ensure that the Allies had sufficient combat power to defeat the Germans.