The logistics of supplying an army, the size of which landed on D-Day and which would engage in the Battle for Normandy and the liberation of France can be imagined!
It was obvious to the Allied Commanders, that a major port would be required to land all the equipment that would be needed. The two ports of any significance in Normandy were, Cherbourg to the west and Le Havre to the east. The Americans favoured Cherbourg.
Intelligence sources reported heavy defences around these ports, it was also anticipated that the German engineers would have been prepared to destroy these facilities, should they be in danger of falling into enemy occupation.

At the Roosevelt-Churchill conference in Quebec in August 1943, it was decided that an artificial harbour would have to be built and towed across from England to France.
The codename for the project would be "MULBERRY"
The size of this undertaking can be imagined!
Winston Churchill issued the order…
We require piers for use on the beaches.
They must float up and down with the tide.
The anchor problem must be mastered.
Do not argue the matter, the problems will argue for themselves.
Let me have the solution worked out.

The solution was worked out and it was decided to build not one harbour, but two!
One for the British, to be constructed at the little coastal town of Arromanches and the other for the American forces, to be built off the coast of Omaha Beach.
All over the U.K. 30,000 men and women were engaged in producing more than one million pre-fabricated parts that would make up the harbours.
99.9% of these people having no idea whatsoever what they were producing, the secrecy was so tight.
The cost of this project was in excess of $100,000,000, at today's prices that would be over "One Billion" dollars.

The "Harbour" would consist of four major components..
The First component was 60 block ships which sailed across the channel under their own steam, when in their correct location, they were lined up, bow to stern and scuttled, therefore creating breakwaters for the harbour.

The Second component was a construction which would form the harbour walls, massive reinforced hollow concrete blocks, called caissons, some, 150 of these were built in various sizes, the largest was 200 feet long and 60 feet tall.
On D-Day 6th. June 1944, the greatest towing job in history took place, 85 tugs each with a caisson started the long haul, at a maximum speed of 5 miles per hour.
Each caisson had a small crew and also an anti-aircraft gun fitted on a platform,
When in the correct location the crew would open the flood valves and the caisson would sink to the sea bed , leaving approx. two thirds above sea level, placed end to end these would form a harbour wall 2 miles long!

Like the fabled "Phoenix" the bird that rose from its own ashes, the concrete caissons could be resurrected by closing its valves and pumping out the water, thus allowing it to be moved to another location.
Many caissons were returned to England, but, most stayed off the coast of Normandy.
Because of its adaptability to be used in this way the constructions were called "Phoenix Caissons"

Continued…...