EM 1110-2-1100 (Part I)
30 Apr 02
assault, details and forecasts of changes must be acquired of coastal type, beach configuration,
morphodynamics, profiles, wave conditions, tides, beach material, beach trafficability, and nearshore and
offshore bottom-holding capacity for moorings and anchored ships. At the start of the war, many charts were
available showing areas safe for deep-draft navigation and details of land topography, but hardly any of the
nearshore areas where assault troops and supplies could be landed. Much of this type of information was
collected and evaluated during the war. Of prime importance to military amphibious operations are the wave
conditions that can be anticipated. Correlations among wind strength, duration, fetch, and wave height and
period were developed in the United States and in the United Kingdom (U.K.) for wave forecast for planning
and for operations. The state-of-the-art in military coastal engineering at the end of W.W. II was documented
in the Manual on Amphibious Oceanography, (University of California at Berkley (UCB), Institute of
Engineering Research (IER) 1952) (Wiegel 1999).
b. Expedient harbors. Expedient harbor design for the invasion of Normandy also required substantial
coastal engineering effort. The design of the two Mulberry harbors ("A" at St. Laurent (Omaha Beach) and
"B" at Arromanches) required information on wave and tide prediction (design tide range was 7.3 meters (24
feet)), wave diffraction, wave induced forces, bottom conditions, and placement of structures and their
foundations. Wave-diffraction theory (wave transmission about the tip or through a gap between
breakwaters) was developed for this project. The Mulberry Harbor was designed in two parts. The portion
closest to shore, in shallow water, had a breakwater of vertical reinforced-concrete caissons (code name
"Phoenix") and sunken ships protecting it, while the seaward portion was protected by moored floating
breakwaters ("Bombardon"). The Bombardon had a cross section similar to a Maltese cross in shape; each
unit was 61 meters (200 feet) in length, 7.6 meters (25 feet) in beam and depth with 5.8 meters (19 feet) draft.
They were deployed in pairs with a 15.2 meters gap between pairs. Located inside the shallow water
sheltered area were pier heads and mile-long pontoon-supported flexible bridges (causeways code named
"whales"). After initial construction, a storm along the Normandy coast with gale winds blowing from the
northeast generated sea conditions larger than project design waves. Operations were disrupted and delayed,
with great damage to the artificial harbors, craft and ships. Mulberry "A" suffered damage beyond repair.
Shown in Figure I-3-14 Is Mulberry "B" after being repaired. The Civil Engineer in War, A Symposium of
Papers on Wartime Engineering Problems, Volume 2, Docks and Harbors (Institute of Civil Engineers 1948)
provides details on the design, installation, and performance of the Mulberry Harbors (Wiegel 1999).
c. Military coastal engineering studies. After W.W. II, UCB contracted with the Office of Naval
Research (ONR) to review amphibious operations reports from the war. As expected, many landing-craft and
amphibious-vehicle casualties were due to enemy action, but many were related to problems with waves and
currents causing capsizing, swamping, broaching, getting stuck on bars and, when the ramps were down,
filling with water and sand. Another major problem was beach trafficability. Vehicles were frequently stuck
in the sand. A trafficability study of beach sand characteristics, beach slope, water level, and vehicle type
was made. It was observed that saturated sand near the water's edge would liquefy due to vibrations
produced by the vehicular traffic. Several full-scale amphibious assault-training exercises were observed in
detail and reports prepared on the observations and findings.
During the 25 October, 1949, exercise across three west coast beaches at the Waianae-Pokai Bay region of
Oahu, Hawaii, long-period waves surging up the steep beach face caused substantial landing craft casualties
on two of the beaches. Many of the craft broached and were shoved onto the steep beach by the surging
breakers (see Figure I-3-15). Of the 20 landing craft sent ashore in 3 "waves" in the first 15 minutes of the
amphibious exercise, 7 retracted and 8 were lost, some filling with water and sand when the ramps were
lowered. The exercise was quickly halted and five of the craft later salvaged. Because of the problems
experienced moving personnel, equipment and supplies through the surf and over the beach, the Department
of Defense began the development of helicopters and air cushion vehicles (Wiegel 1999).
History of Coastal Engineering