Once construction had concluded the myriad components would need to be assembled and sailed across the English Channel to Normandy, both significant feats of organisation, skill and seamanship in their own right.
Getting Ready to Cross the Channel
The diagram below shows the assembly sites and routes.
The assembly task required many Phoenix caissons to be re-floated because they were sunk in various locations for concealment purposes. The Whale roadways were assembled, complete with their Beetle floatation pontoons, and towed across the channel as complete strings.
Bombardon’s were usually towed in pairs.
A force of 132 tugs were used to tow the various parts of the two Mulberry harbours across the English Channel.
Some of these components were lost to weather and enemy action but for the most part, arrived as planned.
Operational security was paramount, the captains of the block ships were told they were going to the Bay of Biscay and a model of the Mulberry harbour and invasion beaches in the headquarters of the Automobile Association at Fanum House was made by toymakers who were confined to the building until well after the invasion.
The construction plan was equally complex, accounting for combat and weather losses, and coordinating with available labour and overall invasion sequence.
The Mulberry construction teams on the UK and US were given the go ahead to sail on the afternoon of the 6th of June, D Day.
First to go were the Mulberry B team, the British No1 Port Construction and Repair Group.Following the relatively light resistance at Arromanches they started work quickly.
The US forces at Omaha were much less fortunate and faced both an array of difficult obstacles and a reinforced defending force but nevertheless, both build teams got cracking, making use of mobile command posts such as the paddle steamer HMS Aristocrat.
Assembly off the Normandy Coast
The first task for the constructions teams was to confirm the initial findings of the covert surveys conducted prior to D Day and then to carry out more extensive surveys for the caissons and pier heads.
Positions were then marked using buoys in readiness for the construction to begin proper.
With surveys complete, the first component to arrive were the block ships, scuttled in overlapping patterns to avoid wave penetration and excessive scour. By the 13th Gooseberry 1 at Utah was complete and as a shelter for small to medium sized ships allowed dry shod unloading of a large number of personnel and material using pontoon causeways before the pier heads were established.
However, against British advice, the US construction team allowed gaps between the block ships to facilitate small craft movement, this would later prove to be a serious mistake. The second Gooseberry was completed during the same week, also at Omaha.
Gooseberry 3 at Arromanches, 4 at Courselle (Juno) and 5 at Ouistreham (Sword) were then completed in short order.
By the 17th June, both Bombardon strings were in place.
Phoenix towing started on the 10th of June, by the 18th, 75 were in position, planted exactly according plan except one that swung out of position as a result of a collision between it and a tug, in the dark.
Pier heads and Whale roadways started to arrive on the 9th of June and by the 14th, vehicles were rolling off ships, onto the pier head and down the roadway towards the beach.
The build operations were not without their fair share of problems; failures and late arrivals competed with unexpected seabed conditions and poor weather to slow things down.
The Great Storm and it’s Aftermath
Between the 19th and 22nd of June, a storm of unprecedented magnitude hit the invasion beaches.
The forecasters did provide some warning that allowed tugs to be stocked with rations, pier heads raised, moorings checked and doubled and all other ships ordered back to England.
The tugs were also armed with PIAT’s and ordered to sink any Bombardon or ship that became a hazard to the Mulberry harbours as it was thought this might be likely.
The storm was actually the worst for 80 years, comparable to that which scattered the Spanish Armada several hundred years earlier.
Damage was considerable.
Many of the Phoenix caissons were overtopped; not a problem in itself but when the tide subsided the internal water pressure caused five of them to burst and one was damaged by scouring.
The Bombardons fared much worse as the weather conditions exceeded their design specification, every single one broke loose. Many hundreds of small craft were tossed around like matchwood and some of the piers were damaged.
Mulberry A was more exposed than B and therefore suffered a great deal more damage.
Pier heads and roadways were smashed. 21 of the 30 Phoenix caissons were destroyed by a combination of severe scouring, internal water pressure and being battered by free floating Bombardon.
The lack of attention to the correct mooring procedures was also thought to be a contributing factor to the damage on the roadways but much of this was also caused by free floating landing craft, 5 of which were actually British. Out of 650 LCT’s in the area, only 330 survived although the DUKW’s were able to ride out the storm by the simple expedient of driving onto the beach.
Damaged ships were cut open to get at their cargo and ships were deliberately beached regardless of their ability to be re-floated, desperate times needed prompt action.
The construction force and a number of US officers with relevant experience of salvage and Mulberry construction thought it could be repaired but more senior officers differed.
The decision was made to salvage what could be used on Mulberry B to aid in its reinstatement.
The Gooseberries at Mulberry A were to be reinforced and the Phoenix caissons at Mulberry B doubled up so they could continue to operate until the Winter, much longer than anticipated. The caissons were also filled with dredged sand, covered with steel sheeting, gaps filled with rock filled steel mesh gabbions.
At Omaha, the Gooseberries were reinforced and this allowed US forces to actually exceed the intended offload rate compared to the original plan.
By D + 30 it was operating at an average of 9,000 tons per day throughput.
Because the piers at Omaha were destroyed LST’s had to be beached but favourable geology and construction work allowed them easier access than previously thought possible.The Rhino ferries, LST’s, landing craft and DUKW’s continued their relentless operations and at times exceeded the offload rate of Mulberry B.
Mulberry B was in almost constant use for 5 months and in excess of 2 million men, half a million vehicles and 4 million tons of supplies were landed.
As Winter approached the larger Liberty Ships were increasingly used instead of the smaller coasters and LST’.
These 7,000 ton ships were offloaded at Mulberry B until the 19th November 1944, when the artificial harbour at Arromanches was closed, it’s war over.