The Floating Harbors of D-Day

this video was made possible by curiosity stream sign up for the nebula bundle deal for just 1479 at curiositystream.com forward slash real engineering to watch the other eight episodes in this logistics of d-day series when learning the history of d-day we are most frequently met with tales of valor of soldiers rushing the beaches our collective vision of that day opens with the lowering of higgins boat ramps on omaha beach the fury and violence of battle taking center stage in this chaotic vision it's hard to believe that what was happening was a carefully choreographed plan one that required hundreds of thousands of people laborers in factories merchant sailors transporting goods across treacherous oceans engineers dreaming up novel solutions to new problems and of course the military strategists that conceived the invasion plans each played their part in the lead-up to d-day by the end of july just a little under two months after the first men came ashore 675 000 personnel were ashore with 150 000 vehicles 690 000 tons of supplies and 69 000 tons of fuel the planning and background support required to make this happen was immense some of these men and supplies were air dropped into the fields of normandy but the vast majority of these supplies were brought ashore by landing craft ranging in size from the personnel landing craft like the iconic higgins boat all the way up to massive ships like the lsd or landing ship tank these behemoths could carry 18 sherman tanks or 33 trucks with births for up to 217 troops these ships would prove invaluable in maintaining the supply chain in normandy however the logistics of direct beach supply came with a host of potential and inevitable delays all of the landing craft like the higgins boat needed shallow drafts to allow them to get close enough to the water's edge to offload their cargo this made them incredibly unstable and in rough seas manny capsized some like the lsds had ballast tanks that could be filled or emptied to alter their draft filling them to increase their draft for the open ocean increasing the ship's stability and emptying them to decrease it and come close to shore yet even lsds faced logistical problems arrive at low tide and you are racing the tide while you unload your cargo into deeper and deeper water arrive at high tide and you are racing the tide as it leaves you stranded on the beach until the next high tide arrives on top of all this the vast majority of war material was coming from the united states aboard liberty ships these ships needed deep water harbors to dock without a harbour of this kind in france liberty ships were forced to dock in britain and transfer their goods to smaller ships like the lsd if these ships could simply dock in france it would save a great deal of time and effort in this logistical supply chain sherberg was prioritized for this very reason its deepwater harbour was a key strategic target and the allies choice of normandy was largely based on its proximity to the contentant peninsula a peninsula which could be cut off from reinforcements from utah beach westward however this campaign would take some time the allies needed a deep water port as soon as possible without a steady stream of supplies and reinforcements the small allied beachhead risked being forced back into the ocean the allies were faced with a difficult dilemma and their solution is one of the most remarkable feats of the second world war two floating harbors were constructed and towed across the english channel to be placed directly onto the beaches of normandy one for the british and one for the americans each with an equivalent capacity to the port of dover this is the story of the mulberry harbors harbors serve some key functions to allow ships to unload their cargo in safety the first role a harbor must fulfill is to act as a safe refuge for the ships protecting them from the chaotic weather of the sea to do this harbors need large break waters and other protection to halt waves in their tracks leaving the inner harbor relatively calm next they must provide water deep enough to allow ships to more directly next to the pier and unload their cargo regardless of the tide levels two simple functions that often require an immense engineering effort dredging of the sea floor to increase the depth of water construction of large concrete structures and general planning often take years to complete yet the challenge the allies faced was much greater than a typical harbour this harbour needed to be built in complete secrecy floated across the english channel and assembled in the middle of a war zone it was an insanely ambitious plan let's see how they did it before making any detailed plans the engineers would need detailed surveys of the ocean floor and this information was vital for the design stage surveying the ocean floor would inform the designers where to locate deep water offloading points for ships how high breakwaters needed to be to rest on the ocean floor and sit above the waves at all tide levels and finally it gave the vital seafloor topology information required to design a floating pier flexible enough to deal with the rough seas and lay on the seafloor without buckling and breaking taking soundings while germans watched and listened from the shore was a job entrusted to the 7th and 12th survey flotilla they made a total of six trips on moonless nights between november 1943 and january 1944 setting sail from cows on the isle of wight data was gathered in two locations here to the east of omaha beach the designated location for the american harbour dubbed mulberry harbour a and here to the west of gold beach the designated location of the british harbour dubbed mulberry harbour b typically three small lcvp landing craft were towed by gunboats across the channel once they reached a point about 48 kilometers off the coast they slipped their toes and began their stealthy approach to the shore these lcvps were modified with underwater exhausts to muffle the sound of the engine tarps to allow the crew to work with light without being seen from the shore and each boat was equipped with echo sounders to survey the ocean floor along with the necessary navigation equipment to match the soundings with coordinates on the map this work provided depth charts like this one which gave the engineers the information they needed to accurately plan the layout of the harbors the first components they needed to address were the breakwaters these would provide shelter to both the ships and floating piers contained within the breakwaters took several forms the simplest being codenamed corncob the allies had a huge inventory of aging ships which were no longer fit for use planners sought ships that were at least 30 years old like the first world war super dreadnought hms centurion a 25 and a half thousand ton ship which had previously been used as a remote control target ship for naval aiming practice in the 1930s it was scuttled as part of the breakwater from mulberry harbour a this was just one of 14 ships that formed what was termed a gooseberry at mulberry harbour a one of these breakwaters was formed at each and every landing beach shielding the landing beach from the worst of the waves and allowing landing craft to unload their wares in relative cam the scuttled ships were also ballasted and sunk in a manner that ensured their superstructure remained above the water line in fact the crews of these ships had no idea of their fate as they set sail for normandy their useful equipment was removed two explosive charges were laid and they were informed of their destination with no further information upon arriving and anchoring off the beaches a wrecking officer boarded their ship and detonated the charges with the men still aboard there the ships sank and the crew members remained at action stations providing valuable first aid refueling and repair services for the smaller boats under their protection the next component of the breakwaters the bombardons were designed for deeper water the designers of the mulberry harbors wanted breakwaters placed further from the coast which would provide some protection to deeper draft ships like liberty ships which would unload their wares onto smaller ships to transport to the beaches these breakwaters underwent several design iterations namely in the quest to reduce the level of concrete and steel required to build them building a structure that lay on the sea floor in water this deep was not feasible so some innovative designs were trialled one idea was a pneumatic breakwater this idea proposed the use of compressed air fed through perforated pipes along the seafloor to create a wall of air bubbles that would block the motion of waves this sounds like an outlandish idea how could air bubbles possibly block the immense power of the sea two surface currents are created with this method one opposes the incident waves and the other inner harbor facing current has no effect on the wave action this was a tried and tested method of creating a breakwater this is a video of the effect in action however it takes an enormous amount of power to pump the volume of air required against the pressure of water bearing down on the pipes estimates of the power required for the two mulberry harbor pneumatic breakwaters were placed at an astonishing 3 million horsepower this being rather obviously unfeasible left the allies with one choice a series of floating breakwaters waves are after all surface phenomenons and an adequately designed floating breakwater can provide shelter once anchored sufficiently rigid floating breakwaters were needed these cross-shaped steel break waters were chosen as they minimized the quantity of steel required even still each one contained 250 tons of steel the bottom three arms were opened to water while the top was enclosed to allow it to float each was 60 meters long and 7.6 meters in both width and depth leaving large gaps between these floating break waters was not an option as the waves would simply pass through the gaps by diffraction and rebuild themselves inside the harbour with most of their energy retained during the design phase the engineers tested a range of gaps optimizing the area covered and the wave transmission and found a 15 meter gap was optimum two rows of these break waters were more 250 meters apart which provided a reduction in wave height by 70 percent and reduction in wave energy by 90 percent these break waters were assembled about two kilometers offshore for both mulberry harbour a and b in the six days after d-day providing liberty ships some protection as they offloaded cargo to smaller ships capable of offloading directly onto the beaches the final line of defense was the phoenix casens these provided the brunt of the protection for the harbour these were essentially boats made of concrete there were six different sizes each tailored for the depth of water they were designed to be sunk in the largest being the a1 type which was 18 meters high 24 meters wide and 63 meters long and weighed an astonishing 6 000 tons these larger casings even had anti-aircraft guns attached to provide anti-aircraft cover for the harbour which was not needed in the end each end of the phoenix casings was upswept to allow for easier towing across the channel the lower level of the concrete boats consisted of a series of water-tight compartments which were flooded to sink them in fact once each casing was complete the allies sunk them offshore to hide them from german planes until the time came to re-float them and transport them across the channel 147 of these phoenix casings were manufactured on beaches excavated basins along the thames and in actual dry docks around britain with a workforce of over 20 000 people taking 150 days to complete the massive breakwaters the skill of these workers varied greatly and as a result the concrete was of varying quality upon sinking many cases broke their backs but at this stage it mattered little their purpose was to sit on the seafloor but removal efforts would prove difficult and to this day many of these massive concrete structures remain in normandy the next portion of the mulberry harbour design the piers required vastly more engineering forethought they needed to function at high and low tide and every level of tide in between that's a great deal of mechanical movement along the length of the pier and that's not even accounting for wave action as the breakwaters couldn't feasibly stop all waves from getting through these structures needed to deal with these forces and managed to provide a steady roadway for trucks filled with supplies and tanks traveling across it it was a huge engineering challenge the first structure needed was an offloading pier this couldn't be a floating platform it needed to be rigid and stable to accommodate the shifting weight of trucks loading cranes and supplies so each platform came with four legs which could be controlled independently of each other each leg could be lowered to the sea floor allowing the pier to lie evenly on the surface even if the sea floor wasn't even the platform was capable of moving up and down these legs at a rate of about 0.75 meters per minute more than enough to quickly adjust to tight levels the platform could float but it was typically kept a short distance above the water to keep wave rocking to a minimum around the four edges of these sput piers were attachment points for floating pontoons that could expand the birthing space for ships like this modular slipway designed to allow lsds to offload their cargo directly from their front ramp each spud pier also had eight bearing seatings to attach bridge spans to the pier these bridge spans were the next challenge the motion of the sea would place rolling pitching and twisting action along the length of these bridges if the bridge was not capable of moving with the ocean it would inevitably break apart the bridge sections were relatively stiff along their length thanks to their h-beam design ensuring the bridge spans could support the 25-ton tanks that would be crossing them the tapered h-beam design where the side girders narrowed towards the ends also allowed the sections to accommodate a great deal of twisting motion up to 40 degrees along its length essential for dealing with the rocking ocean the bridge sections were modular allowing additional length to be added by simply adding additional sections this was achieved through spherical bearings at each end that slotted into seating in pontoons called beetles the bearings were designed to allow 24 degrees of deflection between each section allowing bridge sections to pitch with the ways and accommodate up to 48 degrees slope when laying directly on the seabed to ensure the bridge sections were not simply ripped apart wire cables were attached to the beetle pontoons and wrapped around a hole in the girder's end section these beetles like the phoenix casens were primarily constructed with concrete to save precious steel only pontoons that would be laid over the tidal zone were constructed from steel and once designated for rocky sections of tidal zones also came with adjustable spud legs these flexible floating bridge sections connected the spud piers to the shoreline and allowed them to operate through the full tidal range without issue with all of these components designed tested manufactured and hidden from site the allies were ready as d-day approached the various components were transported to these locations before sailing towards area zebra the entrance point to the shipping lanes the allies had cleared of mines just a day before d-day construction of the breakwaters began on d-day itself mulberry harbor a the american harbour off the coast of omaha beach was the first to begin and finish construction the bombardance anchored down on june 6th and the first phoenix casings were in place by june 9th all corn cob ships were scuttled by june 10th and the entire breakwater was finished on june 11th just five days after d-day by june 18th four spud piers were completed and offloading cargo with two whale and beetle piers connecting them to the shore mulberry harbour b the british harbour was slightly slower in construction by june 18th the eastern pier was completed with four spud pier heads while the center pier and the lsd pier were partially completed these structures were protected by a partially completed break water only 25 of the 82 phoenix casings were in place by june 18th with no protection on the eastern or western flanks of the harbour june 18th is a pivotal date because on june 19th an unprecedented storm arrived in normandy and raged for two days winds tore down from the northeast through the strait of dover with waves as high as 4.5 meters being reported far exceeding the maximum design expectation of 2.4 meter waves it is said that this was the worst storm the region had seen in 40 years the american harbor mulberry a was completely broken beyond repair 21 of the 28 phoenix casings were destroyed with four more being badly damaged the whale and beetle piers were smashed and twisted by the lashing waves seven of the thirteen blocked ships broke their back while others sunk below the waves as a result of the ground below their hulls being swept away bombards and ships alike had broken their moorings and drifted ashore sometimes crashing into the harbour itself and causing further damage mulberry harbour b by some miracle avoided the worst of the waves thanks to the natural breakwater of brochures du calvados located directly in the path of the waves however this did not save the bomber down breakwaters located further to sea these were broken apart completely and manny came ashore to the west of the harbour while six of the 25 cases already in place were destroyed three of the four pure heads were also damaged but not beyond repair parts were scavenged from mulberry a to not only repair mulberry b but to strengthen it mulberry b soon to be dubbed port winston took whale bridges from mulberry a to construct a second store's pier an lsd pier and a shorter pier to allow rhino barges to offload by the end of october 40 000 vehicles and nearly a quarter of a million personnel used this harbour to come ashore while an average of seven thousand tons of supplies were discharged every day an immense effort far exceeding the original plants in fact the harbour operated far beyond its original operational target date breakwaters were reinforced with an additional 40 phoenix casings this extra protection allowed port winston to stay in continual operation through the autumn and winter until its closure in december 1944 by which time the capture of sherborg diep ostend and antwerp made the use of temporary harbours unnecessary detractors of the harbours point out that the us forces managed just fine without the mulberry harbour thanks to a greater than expected performance from the lsds and other landing craft capable of supplying directly onto the beach omaha beach was managing 10 000 tons of supply per day at its peak while port winston achieved 6 750 tons per day at its peak this criticism ignores the need for landing craft in the pacific war an upcoming southern invasion of france not to mention that redundancy and planning for the worst is a vital part of war logistics with a foothold in europe established the allies could begin streaming into the continent two months of intense fighting in normandy was fueled by these supply lines inch by inch the allies scraped forward but by the end of july the tides turned the breakout arrived and the front line began to race ahead of established supply lines operation cobra drove south towards brittany reaching its border by july 31st by august 7th brittany was overrun by august 25th paris was liberated and by september 15th nearly the entirety of france was free while the allies pushed towards the german border but this rapid advance brought with it new problems supply lines from the harbors to the front line were being stretched and they would be on the verge of breaking until antwerp could be captured the allies had been successful in their campaign to german supply lines prior to their invasion but this was the very infrastructure they now need it vital train supply lines would take time to reconstruct and the germans were readying themselves for one final massive counter-offensive the battle of the bulge this battle would test the allied supply lines to the limit and without one simple but pivotal innovation the allies could have been stopped in their tracks the red ball express which is the subject of the final episode of the logistics of d-day series available exclusively on nebula this series has been a passion project of mine for the past nine months and the episode you watch today has featured tidbits from each of the nine episodes we have an entire episode on why normandy was chosen which is also available here on youtube the seven others are exclusive to nebula and include episodes on the deception tactics to keep things like the mulberry harbour secret an episode detailing the methods the allies used to clear away through the minefields of the english channel and subsequently punching a hole in fortress europe an episode each for the amphibious and airborne landing operations one detailing the close air support logistics where engineering battalions rushed ashore on d-day to construct new airfields another detailing the insane oil supply pipelines that were laid across the english channel on d-day this series which is over two hours long in total would not have been possible without the funding and support of curiosity stream and nebula the streaming platform i created with over 100 of my fellow youtube creators the best way to watch and ensure that future projects like this can be funded is by signing up for the curiosity stream a nebula bundle deal here you'll get a year's access to both platforms for just 14.79 a year an insane deal that will get you access to this series ad-free videos from your favorite youtube creators nebula exclusives like tom scott's money and access to curiosity streams award-winning documentaries like this one called hidden traces which explores the scars of d-day still present in normandy like those massive concrete breakwaters many of which remain in the shallow waters of the sien bay to this day for now we are taking a break from this series and we'll begin working on upgrading our animation abilities and researching for season two we want to hear your suggestions for the next battle we should focus on but for now i am veering towards covering the logistics of the battle of britain an aerial war that tested two nations ability to not only build planes and train pilots but tested their wartime planning and strategy a decisive battle that turned the tide of world war ii and prevented the germans from gaining the air superiority needed to begin their own amphibious invasion of britain if you want to see that please sign up for the curiosity stream enable a bundle deal as always thanks for watching and thank you to all my patreon supporters if you'd like to see more from me the links to my twitter instagram discord server and subreddit are below

Channel: Real Engineering

Views: 425,050

Rating: 4.9526739 out of 5

Keywords: engineering, science, technology, education, history, real

Id: zpFLLGkNm7I

Length: 24min 55sec (1495 seconds)

Published: Sat Oct 10 2020