I've been in two minds as to whether this warrants a report or not considering it's a museum, but seeming as the only mention of it I can find on the forums is in a similar report on the Blockhouse Museum in Eperlecques, I thought I'd give it a shot. I did have a mooch around the carnage left up top from the Allied bombing raids after all...
Background
The Multi-Charge Concept
In a traditional artillery gun, the size and power of the gun is dictated by the weight of the breech, because peak pressure is achieved upon detonation of the propellant, so the breech must be strong enough to contain this. There comes a point when this weight becomes untenable, imposing a limit on the power guns could reasonably reach, although there are exceptions such as the Schwerer Gustav Railway Gun. However, it's sheer size, level of preparation needed to transport and use it, and the massive man power requirements severely limited it's usefulness, reinforcing this point. Pressure gradually drops as the shell travels down the barrel, which also limits power.
A Multi-Charge gun fires a shell with a low powered charge, so it doesn't require a heavy breech due to the low pressure. Instead, it uses multiple charges which would detonate as the projectile travelled up the barrel, maintaining peak pressure and increasing its velocity. This, along with its ballistic trajectory, would allow the projectiles to travel extremely long distances.
The idea was first devised in the mid 19th century by Americans Haskell and Lyman, who developed a prototype for the US Army, which was unsuccessfully tested at the Frankford Arsenal in Philadelphia. It underwent further refinement and testing, but only managed to achieve a muzzle velocity of 335m/s, which was inferior to conventional artillery pieces of the time, so the idea was abandoned. Louis-Guillaume Perreaux, a French engineer, was also working on the same concept, being granted a patent in 1864, and presenting a prototype at the 1878 World Exhibition of Paris.
The Haskell Lyman Prototype -
No further development occured until 1918 during WW1, when the French Army drew up plans for a long range Multi-Charge gun as a response to the German Paris Gun. These never came to fruition due to the Armistice, and were subsequently shelved.
The Development of the V3
With the fall of France in 1940, the German troops discovered the WW1 plans, with the patent acquiring the attention of August Cönders, the chief engineer of the Röchling Stahlwerk AG manufacturing plant in Wetzlar, by 1942. He realised that the Multi-Charge concept could solve the issue of premature wear on the barrels of long range guns, with super long range guns such as the Schwerer Gustav Railway Gun wearing through barrels in as little as 300 shells.
Cönders proposed the use of electronically controlled charges in the side chambers in order to eliminate the risk of premature ignition which plagued the Lyman-Haskell gun in the previous century. He quickly manufactured a working 20mm prototype at Wetzlar using the readily available machinery, as this plant was responsible for producing the 20mm barrels for the Flak 38.
The idea was presented to Albert Speer, who subsequently proposed it to Hitler in May 1943. Work was authorised to continue, with the gun becoming Hitler's third Vergeltungswaffe (Vengeance Weapon). Development took place under the code name of Hockdrockpumpe (High Pressure Pump (HDP for short)) in order to conceal the project's true purpose from the Allies.
After the RAF bombed the Peenemünde rocket center on 17 August, Hitler agreed to Speer's suggestion that the gun be built without more tests. Cönders constructed a full-calibre gun at the Hillersleben proving ground near Magdeburg but, by the end of 1943, he had encountered severe problems both in putting the gun's basic principle into operation and in producing a feasible design for the shells that it was to fire. Even when everything worked, the muzzle velocity was just over 1,000 metres per second, which was nowhere near what had been promised.
Nonetheless, a proposal was made to build a single full-sized gun with a 150-metre barrel at Misdroy on the Baltic island of Wolin, near Peenemünde, while construction went ahead at the Mimoyecques site in France, which had already been attacked by the USAAF and the RAF. The Heereswaffenamt (Weapon Procurement Office) took control of the project by March 1944, and, with no good news from Misdroy, Cönders became one of the engineers working on the three chief problems: projectile design, obturation (prevention of gas blow by), and premature ignition of the secondary charges.
The obturation issue proved to be a relatively simple fix. A piston was placed between the projectile and the initial propellant charge which provided a seal, preventing the gases from overtaking the projectile. This also solved the secondary charge ignition problems, negating the need for any improvements there. By May 1944, there were four viable designs for a 150mm finned projectile, with the Sprenggranate 4481 design being adopted. Trials were held at Misdroy between 20-24 May, achieving a maximum range of 55 miles. A further trial on the 4th July achieved a 58 mile shot, but the gun barrel burst preventing any further tests.
The Misdroy Prototype Gun -
The V3's Final Design
The design was made as simple as possible for ease of production, with each section of barrel and side chambers being identical enabling any damaged sections to quickly be swapped out. The gun wasn't designed to be movable, so weapons sites were to be laid out with the guns trajectory permanently aimed at the selected target (London in the case of Mimoyecques).
Rather than using conventional explosive charges, solid fuel rocket boosters were chosen due to their suitability and ease of use, with them being arranged in symmetrical pairs along the barrel which were angled to direct their thrust against the base of the projectile as it passed. The cannon had a smoothbore barrel which fired the Sprenggranate 4481 projectile, which relied on aerodynamic forces rather than gyroscopic forces (as imparted by the rifling in a rifled barrel) to keep stable flight.
The Mimoyecques Site
The site was chosen in 1943 due to its geology, with the Limestone hill being perfect for the necessary tunnel complex to house and service the guns. The Chalk was easy to dig through, whilst being strong enough to not require additional support. It was in the Pas-de-Calais region in order to target London, and was nearby to numerous V1 and V2 launch sites which were also under construction.
Construction by Organisation Todt began in September 1943 with railway lines built to support the work. Two sites were to be built around 1km apart, each with five Gun Shafts that would house five HDP guns apiece, meaning a total of fifty guns which would allow 600 shells per hour to be fired towards London.
A Photo Map of the sites -
Work was focused on both complexes initially, although work was abandoned on the Western Complex by November after work was disrupted by Allied bombing raids. The aim was to have one five gun battery operational by March 1944 and the entire Eastern Complex complete by October 1944.
Work on the Gun Shafts began in October 1943 with the work progressing quickly. The shafts were dug at a 50 degree angle on a bearing of 299 degrees, providing a direct line on Westminster Bridge. They reached a depth of 105 metres beneath the hillside, exiting through a 5.5m thick concrete slab with a steel plate protecting each exit.
One of the Adit Exits, prior to demolition by the Royal Engineers -
Armoured doors were installed on the railway tunnel portals. An extensive network of tunnels and elevator shafts were dug, and had the site become operational, it would have housed around 1,000 troops of the Artillerie Abteilung 705 division.
Site Plans -
The scope of the work was reduced owing to the difficulties in perfecting the prototype gun, with the I and II drifts being abandoned. The armament was also reduced, with three HDP guns instead of five for each drift. The railway tunnel was 630m long and fitted with a loading platform throughout on the western side. The platform serviced ten cross galleries, each of which were laid with 600mm narrow gauge track for the unloading of ammunition and supplies. The eastern side of the tunnel gave access to multiple chambers which would have housed offices, stores and quarters for the garrison.
Construction work was abandoned shortly after a bombing raid by the Dambusters on the 6th July 1944 with Tallboy bombs causing major damage to the complex, entombing around 300 Germans and forced labourers. A direct hit was scored on adit IV, with the Tallboy penetrating and wreaking havoc below upon detonation, collapsing the adit.
The site remained manned, but was threatened with being overrun by Allied Forces as they moved up the coast from Normandy, with it eventually being captured by the Canadian 3rd Infantry Division on the 5th September 1944. There was no resistance, as the Germans had withdrawn from the area a few days prior.
The complex was rendered completely unusable in May 1945 by means of explosives planted by the Royal Engineers on direct orders from Churchill, much to the consternation of the French as they were not consulted beforehand. Ten tons of explosives were packed into the tunnel and detonated on the 9th May, but failed to achieve the desired level of destruction. A further 25 tons of explosives were used to collapse the tunnel portals, successfully sealing the site off.
This action was taken as it was still seen as a threat to Britain if it were to fall into Soviet hands, the logic of which seems a little flawed to me, because if the Soviets had managed to steam roll their way across Europe to the Pas-de-Calais region, I'd imagine an incomplete bunker with no weaponry would be the least of our worries.
The southern entrance was dug out in 1969 for the creation of a mushroom farm. This was short-lived though, with the entrance being bricked up again by the 1970s. It was decided to open the site as a museum, and efforts were made to clear the tunnels out, with the site opening in 1984. It has remained open to the public ever since, except for a brief period in the 2000s when it had a change in ownership.
The Bombardment of Luxembourg
The project was handed over to the SS in late 1944, and two half length HDP guns were built at Lampaden. It was a much simpler battery design unlike the grand scale of the Mimoyecques bunker. The guns were mounted on steel supports angled at 34 degrees aimed towards Luxembourg, and a couple of blockhouses were built between the guns, along with some smaller bunkers for storage of projectiles and propellant.
The first gun was ready on 30 December 1944, firing two test rounds and then five high explosive rounds. A discarding sabot was used on the projectiles, which weighed in at 95kg and carried a 7-9kg explosive charge. The gun had 12 pairs of side chambers and was able to accelerate the projectiles to a speed of 935m/s. The second gun was operational by the 11 January.
The battery was only operational for a short timeframe, firing 183 rounds with the final shot on the 22nd February 1945 when the Americans were within 3km of the site. Of these, 142 found their mark, killing 10 and wounding 35 people in Luxembourg. The site was dismantled and although there were plans for numerous other sites, the state of the German Railway network prevented any of these from coming online. There were four HDP guns floating around during the allied advance, all of which ended up abandoned at the Röchling Works in Wetzlar, along with remaining ammunition and spares.
The US Army recovered the guns, and they were shipped back to the US for testing and evaluation at the Aberdeen Proving Ground in Maryland before being scrapped in 1948.
The Explore
Not much to say initially... it's a museum... it was raining when we arrived? There are the remains of one of the original steel caps for the guns as you approach the tunnel, which was cast for the originally planned five barrel per adit arrangement. I think it was found in Storage in a nearby Quarry and was gifted to the museum iirc.
The museum is situated on the south side of the complex, and is accessed via the southern portal of the railway tunnel.
The level appears to have been raised slightly from what would have been trackbed level, as there are the remains of the loading platform edges down one side, but it seems a tad too low.
There's not all that much to be seen, other than appreciating the sheer scale of the construction that went into the place, and to think that it was abandoned without ever being completed and becoming operational is mental.
There's a hole as you follow the tour route, I believe it could be the remains of a construction shaft that partially collapsed during the raids. It just looks like a hole in the roof with very little to be seen with the level of lighting provided by the museum, which is why you take a proper torch with you...
It's also fenced off, so had to wait for other people to move on before getting some decent angles. There are what appears to be the remains of possibly handholds, or some sort of mounting brackets along with cable/rope further up. It also appears to maybe lead to another level above, although there's no access to any other levels throughout the museum.
Reached the furthest point into the complex that is accessible which is Gallery 2. The five adits passed through here on their way to the surface. A barrel has been installed in what I believe is the remains of Adit IV to illustrate what the guns would have looked like passing through.
V3 Cannon Replica -
Charge Chambers -
Gallery 2 beyond Adit V -
Gallery 2 towards Adit I and II -
Adit III has natural daylight shining down from the surface, which was quite photogenic. More on this particular hole later though...
Continued around, and there was a gated off section with what looked like the underside of a staircase going somewhere, wasn't skinny enough to squeeze through the gap, and there was too many people around to be jumping it, so couldn't get a closer look.
Came back to the main railway tunnel, and there's another section that's gated off, probably around the same length as what's open, I'm not sure how much more is down there, but apparently it's opened up on special days and for private bookings if you provide notice and have a certain number of people. I'd imagine it's more of the same really, as it is beyond the gun adits, and there are numerous collapses in Gallery 2.
There is a strange lighting choice down this section, it looks like it belongs in Independence Day -
Some carts in a cross gallery -
Insulators -
A calcite deposit -
Possible damage from gunfire -
There's a generator residing in the railway tunnel (I forgot to grab a proper shot of the whole thing) -
There's no way down to the lower levels due to the damage caused by the Royal Engineers, however, considering how well the rest of the complex held up to air raids with the likes of Tallboy bombs being dropped on it, if they were to try digging out some debris, I reckon they may find more of the complex intact... how safe that would be is another question.
We left and found a place to send the drone over the woods to get a view above, and you can see the amount of surface damage inflicted by Allied raids, there are bomb craters everywhere, and you can see how battered the roof of the complex is.
Bomb Craters -
The 5.5m Thick Concrete Slab -
We also spied a way to walk up to it, so that was next on the agenda.
Made our way down and got up close and personal with the devastation.
One of the holes, you can clearly see down a good distance... I believe this particular hole marries up to the chamber where we could see daylight in the galleries below meaning it's the remains of Adit III.
Didn't get a decent shot of the view down unfortunately, as it was a bitch to try and light from a somewhat safe position. It's centre left in the shot below. Note the shape of the concrete opposite, it's the remains of one of the Adit Exits -
We didn't hang around in the area too long in case anyone turned up, so we scarpered and headed off to find some V1 sites.
Thanks for looking.
Background
The Multi-Charge Concept
In a traditional artillery gun, the size and power of the gun is dictated by the weight of the breech, because peak pressure is achieved upon detonation of the propellant, so the breech must be strong enough to contain this. There comes a point when this weight becomes untenable, imposing a limit on the power guns could reasonably reach, although there are exceptions such as the Schwerer Gustav Railway Gun. However, it's sheer size, level of preparation needed to transport and use it, and the massive man power requirements severely limited it's usefulness, reinforcing this point. Pressure gradually drops as the shell travels down the barrel, which also limits power.
A Multi-Charge gun fires a shell with a low powered charge, so it doesn't require a heavy breech due to the low pressure. Instead, it uses multiple charges which would detonate as the projectile travelled up the barrel, maintaining peak pressure and increasing its velocity. This, along with its ballistic trajectory, would allow the projectiles to travel extremely long distances.
The idea was first devised in the mid 19th century by Americans Haskell and Lyman, who developed a prototype for the US Army, which was unsuccessfully tested at the Frankford Arsenal in Philadelphia. It underwent further refinement and testing, but only managed to achieve a muzzle velocity of 335m/s, which was inferior to conventional artillery pieces of the time, so the idea was abandoned. Louis-Guillaume Perreaux, a French engineer, was also working on the same concept, being granted a patent in 1864, and presenting a prototype at the 1878 World Exhibition of Paris.
The Haskell Lyman Prototype -
No further development occured until 1918 during WW1, when the French Army drew up plans for a long range Multi-Charge gun as a response to the German Paris Gun. These never came to fruition due to the Armistice, and were subsequently shelved.
The Development of the V3
With the fall of France in 1940, the German troops discovered the WW1 plans, with the patent acquiring the attention of August Cönders, the chief engineer of the Röchling Stahlwerk AG manufacturing plant in Wetzlar, by 1942. He realised that the Multi-Charge concept could solve the issue of premature wear on the barrels of long range guns, with super long range guns such as the Schwerer Gustav Railway Gun wearing through barrels in as little as 300 shells.
Cönders proposed the use of electronically controlled charges in the side chambers in order to eliminate the risk of premature ignition which plagued the Lyman-Haskell gun in the previous century. He quickly manufactured a working 20mm prototype at Wetzlar using the readily available machinery, as this plant was responsible for producing the 20mm barrels for the Flak 38.
The idea was presented to Albert Speer, who subsequently proposed it to Hitler in May 1943. Work was authorised to continue, with the gun becoming Hitler's third Vergeltungswaffe (Vengeance Weapon). Development took place under the code name of Hockdrockpumpe (High Pressure Pump (HDP for short)) in order to conceal the project's true purpose from the Allies.
After the RAF bombed the Peenemünde rocket center on 17 August, Hitler agreed to Speer's suggestion that the gun be built without more tests. Cönders constructed a full-calibre gun at the Hillersleben proving ground near Magdeburg but, by the end of 1943, he had encountered severe problems both in putting the gun's basic principle into operation and in producing a feasible design for the shells that it was to fire. Even when everything worked, the muzzle velocity was just over 1,000 metres per second, which was nowhere near what had been promised.
Nonetheless, a proposal was made to build a single full-sized gun with a 150-metre barrel at Misdroy on the Baltic island of Wolin, near Peenemünde, while construction went ahead at the Mimoyecques site in France, which had already been attacked by the USAAF and the RAF. The Heereswaffenamt (Weapon Procurement Office) took control of the project by March 1944, and, with no good news from Misdroy, Cönders became one of the engineers working on the three chief problems: projectile design, obturation (prevention of gas blow by), and premature ignition of the secondary charges.
The obturation issue proved to be a relatively simple fix. A piston was placed between the projectile and the initial propellant charge which provided a seal, preventing the gases from overtaking the projectile. This also solved the secondary charge ignition problems, negating the need for any improvements there. By May 1944, there were four viable designs for a 150mm finned projectile, with the Sprenggranate 4481 design being adopted. Trials were held at Misdroy between 20-24 May, achieving a maximum range of 55 miles. A further trial on the 4th July achieved a 58 mile shot, but the gun barrel burst preventing any further tests.
The Misdroy Prototype Gun -
The V3's Final Design
The design was made as simple as possible for ease of production, with each section of barrel and side chambers being identical enabling any damaged sections to quickly be swapped out. The gun wasn't designed to be movable, so weapons sites were to be laid out with the guns trajectory permanently aimed at the selected target (London in the case of Mimoyecques).
Rather than using conventional explosive charges, solid fuel rocket boosters were chosen due to their suitability and ease of use, with them being arranged in symmetrical pairs along the barrel which were angled to direct their thrust against the base of the projectile as it passed. The cannon had a smoothbore barrel which fired the Sprenggranate 4481 projectile, which relied on aerodynamic forces rather than gyroscopic forces (as imparted by the rifling in a rifled barrel) to keep stable flight.
The Mimoyecques Site
The site was chosen in 1943 due to its geology, with the Limestone hill being perfect for the necessary tunnel complex to house and service the guns. The Chalk was easy to dig through, whilst being strong enough to not require additional support. It was in the Pas-de-Calais region in order to target London, and was nearby to numerous V1 and V2 launch sites which were also under construction.
Construction by Organisation Todt began in September 1943 with railway lines built to support the work. Two sites were to be built around 1km apart, each with five Gun Shafts that would house five HDP guns apiece, meaning a total of fifty guns which would allow 600 shells per hour to be fired towards London.
A Photo Map of the sites -
Work on the Gun Shafts began in October 1943 with the work progressing quickly. The shafts were dug at a 50 degree angle on a bearing of 299 degrees, providing a direct line on Westminster Bridge. They reached a depth of 105 metres beneath the hillside, exiting through a 5.5m thick concrete slab with a steel plate protecting each exit.
One of the Adit Exits, prior to demolition by the Royal Engineers -
Site Plans -
The scope of the work was reduced owing to the difficulties in perfecting the prototype gun, with the I and II drifts being abandoned. The armament was also reduced, with three HDP guns instead of five for each drift. The railway tunnel was 630m long and fitted with a loading platform throughout on the western side. The platform serviced ten cross galleries, each of which were laid with 600mm narrow gauge track for the unloading of ammunition and supplies. The eastern side of the tunnel gave access to multiple chambers which would have housed offices, stores and quarters for the garrison.
Construction work was abandoned shortly after a bombing raid by the Dambusters on the 6th July 1944 with Tallboy bombs causing major damage to the complex, entombing around 300 Germans and forced labourers. A direct hit was scored on adit IV, with the Tallboy penetrating and wreaking havoc below upon detonation, collapsing the adit.
The site remained manned, but was threatened with being overrun by Allied Forces as they moved up the coast from Normandy, with it eventually being captured by the Canadian 3rd Infantry Division on the 5th September 1944. There was no resistance, as the Germans had withdrawn from the area a few days prior.
The complex was rendered completely unusable in May 1945 by means of explosives planted by the Royal Engineers on direct orders from Churchill, much to the consternation of the French as they were not consulted beforehand. Ten tons of explosives were packed into the tunnel and detonated on the 9th May, but failed to achieve the desired level of destruction. A further 25 tons of explosives were used to collapse the tunnel portals, successfully sealing the site off.
This action was taken as it was still seen as a threat to Britain if it were to fall into Soviet hands, the logic of which seems a little flawed to me, because if the Soviets had managed to steam roll their way across Europe to the Pas-de-Calais region, I'd imagine an incomplete bunker with no weaponry would be the least of our worries.
The southern entrance was dug out in 1969 for the creation of a mushroom farm. This was short-lived though, with the entrance being bricked up again by the 1970s. It was decided to open the site as a museum, and efforts were made to clear the tunnels out, with the site opening in 1984. It has remained open to the public ever since, except for a brief period in the 2000s when it had a change in ownership.
The Bombardment of Luxembourg
The project was handed over to the SS in late 1944, and two half length HDP guns were built at Lampaden. It was a much simpler battery design unlike the grand scale of the Mimoyecques bunker. The guns were mounted on steel supports angled at 34 degrees aimed towards Luxembourg, and a couple of blockhouses were built between the guns, along with some smaller bunkers for storage of projectiles and propellant.
The first gun was ready on 30 December 1944, firing two test rounds and then five high explosive rounds. A discarding sabot was used on the projectiles, which weighed in at 95kg and carried a 7-9kg explosive charge. The gun had 12 pairs of side chambers and was able to accelerate the projectiles to a speed of 935m/s. The second gun was operational by the 11 January.
The battery was only operational for a short timeframe, firing 183 rounds with the final shot on the 22nd February 1945 when the Americans were within 3km of the site. Of these, 142 found their mark, killing 10 and wounding 35 people in Luxembourg. The site was dismantled and although there were plans for numerous other sites, the state of the German Railway network prevented any of these from coming online. There were four HDP guns floating around during the allied advance, all of which ended up abandoned at the Röchling Works in Wetzlar, along with remaining ammunition and spares.
The US Army recovered the guns, and they were shipped back to the US for testing and evaluation at the Aberdeen Proving Ground in Maryland before being scrapped in 1948.
The Explore
Not much to say initially... it's a museum... it was raining when we arrived? There are the remains of one of the original steel caps for the guns as you approach the tunnel, which was cast for the originally planned five barrel per adit arrangement. I think it was found in Storage in a nearby Quarry and was gifted to the museum iirc.
There's not all that much to be seen, other than appreciating the sheer scale of the construction that went into the place, and to think that it was abandoned without ever being completed and becoming operational is mental.
There's a hole as you follow the tour route, I believe it could be the remains of a construction shaft that partially collapsed during the raids. It just looks like a hole in the roof with very little to be seen with the level of lighting provided by the museum, which is why you take a proper torch with you...
Reached the furthest point into the complex that is accessible which is Gallery 2. The five adits passed through here on their way to the surface. A barrel has been installed in what I believe is the remains of Adit IV to illustrate what the guns would have looked like passing through.
V3 Cannon Replica -
Charge Chambers -
Gallery 2 beyond Adit V -
Gallery 2 towards Adit I and II -
Adit III has natural daylight shining down from the surface, which was quite photogenic. More on this particular hole later though...
Continued around, and there was a gated off section with what looked like the underside of a staircase going somewhere, wasn't skinny enough to squeeze through the gap, and there was too many people around to be jumping it, so couldn't get a closer look.
Came back to the main railway tunnel, and there's another section that's gated off, probably around the same length as what's open, I'm not sure how much more is down there, but apparently it's opened up on special days and for private bookings if you provide notice and have a certain number of people. I'd imagine it's more of the same really, as it is beyond the gun adits, and there are numerous collapses in Gallery 2.
There is a strange lighting choice down this section, it looks like it belongs in Independence Day -
Some carts in a cross gallery -
Insulators -
A calcite deposit -
Possible damage from gunfire -
There's a generator residing in the railway tunnel (I forgot to grab a proper shot of the whole thing) -
There's no way down to the lower levels due to the damage caused by the Royal Engineers, however, considering how well the rest of the complex held up to air raids with the likes of Tallboy bombs being dropped on it, if they were to try digging out some debris, I reckon they may find more of the complex intact... how safe that would be is another question.
We left and found a place to send the drone over the woods to get a view above, and you can see the amount of surface damage inflicted by Allied raids, there are bomb craters everywhere, and you can see how battered the roof of the complex is.
Bomb Craters -
The 5.5m Thick Concrete Slab -
We also spied a way to walk up to it, so that was next on the agenda.
Made our way down and got up close and personal with the devastation.
Didn't get a decent shot of the view down unfortunately, as it was a bitch to try and light from a somewhat safe position. It's centre left in the shot below. Note the shape of the concrete opposite, it's the remains of one of the Adit Exits -
We didn't hang around in the area too long in case anyone turned up, so we scarpered and headed off to find some V1 sites.
Thanks for looking.
