Mulberry Harbours Explained

During the invasion planning in 1943 it was estimated that the allies would require 12,000 tons of supplies a day to be unloaded to sustain the liberating force as it crossed France. The ambitious invasion plan avoided well defended ports and therefore called for two temporary ports.

A composite photograph of Mulberry Harbour B at Arromanches in France. Remains of several elements are still visible today.  

These Harbours known as Mulberry A to serve the American landing Beaches and Mulberry B serving  the British and Canadian Beaches consisted of several elements given the following Codewords or names:

Bombardons: A floating steel outer breakwater.

Phoenix Caissons: A concrete structure anchored to the sea floor forming a fixed breakwater. These came in several different designs.

Corncobs: Ship sunk to form an initial breakwater. 

Gooseberry: The breakwaters consisting of 42 Corncobs, 24 at Mulberry A and 18 at Mulberry B. 

Whales: The Pierhead and roadway system. 

Spuds: Legs fitted to Pierheads used for the unloading of ships. Pierheads have also been known as Spud Pierheads or Lobnitz Pierheads after the company that inspired the design.

Spud Pierhead: A floating adjustable pier anchored by four legs or Spuds. A series of Pierheads were joined together to form the main dock area.

LST Pierhead: A series of Pierheads modified with an upper ramp and buffer pontoon placed in a "T" configuration that enabled LSTs to be unloaded simultaneously from the Bow door and upper deck.

Barge Pierhead: A series of Pierheads specifically for the use of Landing Craft, Barges, (LCB) used for ferrying stores and equipment within the harbour.

Beetles: Floats/Pontoons for supporting the Whale Bridge spans that form the roadway to the beach.

Whale Tows: A series of Bridge Spans mounted on Beetles in Britain for towing to Normandy to reduce time with construction. There were two types of roadways. A 25 ton roadway and a 40 Ton roadway with uprated Bridge Spans and larger Beetles 

Flexible Whale Bridge Span: Placed in every Tow section allowing for the approximate measurements from the pier heads to the shore. they were also used to bridge Pierheads.

Errection Tank or Camel: A large steel tank fitted to the last bridge span in a Tow to facilitate attachment to the next Tow section. 

Buffer Pontoon: a steel pontoon that when attached to a Pierhead forms a sloping surface or artificial beach for unloading Landing Ship, tank (LST) and Landing Craft, tank (LCT) vessels. It is shaped in the form of a hyperbolic paraboloid.

Intermediate Pontoon: Large pontoons placed between Pierheads forming a continuous dock.

Shore Ramp float: to enable vehicles to reach the beach level. Where there were inclines, sections of pre-existing modular Bailey Bridge system were used. These floats were fitted to some Tows instead of an errection tank.

Slug: A small motor boat used to tow Shuttles and men around during construction. They were designed to be able to pass under the Bridge Spans and two were transported to Normandy on davits on each Shore Ramp Float.

Shuttle: a small twin hulled wooden boat with a wire cable drum fitted in the centre. The vessel was used for attaching cables to Bridge Spans and Beetles, joining Tows and anchoring Beetles. Shuttles, Kite Anchors and spare cable drums were transported to Normandy on Whale Tows. 

Kite Anchor: A unique anchor designed to fix the beetles in place.  

The following items are not strictly part of the Mulberry Harbour design, but became an essential part of the logistical effort:

D.U.K.W or Duck:  An amphibious truck, that became a better than expected asset for transporting stores from ships to shore.

Rhino Ferry: A large mobile pontoon powered by outboard motors used to transport vehicles from ships to shore.

Magic Boxes or Advance Base Sectional Dock: a modular system of steel boxes that could be used to form Rhino Ferries or pontoons to reach from LSTs to the shore. These were used by US forces after Mulberry A was destroyed.

The following animation provides an accurate representation of Mulberry B in action.

Click on the image to play the film on YouTube

More information will be added to this page over time.

Further research is ongoing as part of the D-Day Pioneers to Future Innovators Project. you can see the Langstone Harbour, Hayling Island Mulberry Phoenix caisson construction site on Virtual Tour One.