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"Britannia's Eventide" - free-to-download short story set in 1914

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Monday 17th October 2016

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Mallet's Monster Mortar - and the Birth of Seismology

Today the Crimean War (1854-56) is remembered for organisational and tactical incompetence that led to spectacular disasters such as the Charge of the Light Brigade at Balaclava, and the less spectacular, but more deadly large-scale losses resulting from poor logistics and inadequate medical care.  Though limited operations were conducted in the Baltic, the focus of the allied British, French and Turkish forces arraigned against Russia were concentrated in capture of the huge naval base of Sebastopol in the Crimea. The conflict developed into an extended siege, in which allied forces were faced with the reduction of well-engineered Russian fortifications. Enduring the savage winter of 1854-55 in exposed trenches, the besiegers suffered appalling losses from cold and disease and their artillery was to prove inadequate in blasting breaches through which successful assaults could be launched. Though major fortifications known as the “Great Redan” and “The Malakoff Redoubt” were finally stormed by the British and French respectively in September 1855, the cost in lives was appalling.

                                Sebastopol defences - seem from Russian side
                      A panoramic paiting by the Russian artist Franz Rouobaud 

One of the major lessons of the war – indeed one that was learned early on during the Sebastopol siege – was that more effective artillery was required. This was especially the case as regards mortars, capable of supplying plunging fire which would rain down destruction not only on walls, but the defenders behind them.


It is at this point – in the early stage of the war – at which one of the unjustly-forgotten technological giants of the Victorian period enters the story. Robert Mallet (1810 – 1881), was born in Dublin, on 3 June 1810, the son of the owner of an iron foundry. In 1830 Mallet graduated in science and mathematics at Trinity College, Dublin, and thereafter worked with his father to build their business into one of Ireland’s most important engineering companies. Notable achievements were supply of ironwork for the expanding railway network, for the first Fastnet Rock lighthouse and for a swing bridge over the River Shannon.


In parallel with these business interests Mallet developed an interest in earthquakes and in 1846 presented a paper to the Royal Irish Academy "On the Dynamics of Earthquakes". This is now considered to be one of the foundations of modern seismology – indeed Mallet is credited with coining the word "seismology" as well as “epicentre”. Mallet was particularly interested in assessing the energy unleashed by earthquakes and with his son John undertook a series of experiments on how sound or energy moves through sand and rock. The most important of these laid the foundation of modern seismic techniques used in exploration of oil and gas reserves.  In this, a keg of gunpowder was buried on Killiney Beach, south of Dublin, and then detonated. Using a primitive form of seismometer half a mile away Mallet measured the resulting energy wave, thus demonstrating its ability to travel though sand and rock.

                                      RAF personnel with 22,000 lb "Grand Slam" 1945

It is probably Mallet’s insight into the effects of a deep explosion that led to his proposal in late 1854, when the Siege of Sebastopol was still in its early stages, for the creation of a giant mortar. His reasoning may have been similar to that of the great British engineer, Barnes Wallis, which led to the development of the 22000 lb “Grand Slam” bomb of WW2. Dropped from an aircraft, such bombs were designed to detonate only after they had penetrated deep in the ground, thus setting off a local earthquake. They proved especially effective in demolishing hard-to-hit targets such as railway viaducts since a direct hit was not necessary, the earthquake effect being sufficient to bring them down. In Mallet’s day aircraft were not available and the only way of achieving a similar effect was to lob a bomb sufficiently high in the air – and for this a mortar was required.

Mallet recognised that the bomb thrown by such a mortar needed to be massive – he was thinking in terms of a ton, more than had been ever attempted previously – and the mortar itself must be also be enormous and likely to be too heavy for deployment in the field. It was now that Mallet brought his iron-founder’s insights into play and he designed a mortar which would be made up of multiple parts - each large in its own right, but transportable with the means then available – and assembled close to the target. The illustration below shows the construction of the barrel. The bore was 36 inches and the total weight came to 42 tons.

There was little official interest in the proposal initially but in March 1855, with the siege dragging on with little immediate hope of success, Mallet approached the Prime Minister, Lord Palmerston. He was impressed and he instructed the Army’s Board of Ordnance to arrange construction of two weapons. Completion of the mortars was to prove longer than the siege itself – not least because of bankruptcy of the company initially contracted to provide them, and the letting of the work to three others. The weapons were finally delivered for testing in May 1857, over a year after the war had ended.

                                          Mallet Mortar on testing range 1857
 

Nineteen bombs were fired during three separate testing rounds, each being brought to an end by damage to the mortar. A rate of four firings per hour was achieved. The bombs varied in weight between 2,352 and 2,940 pounds – well over a ton. An 80 pound firing charge propelled the lighter shell 2,759 yards (Over a mile and a half, two and a half kilometres) and the flight time was 23 seconds. The conclusion from the testing was that the weapons were not usable. This may well have been due to the metallurgical limitations of the time, for the concept was valid. Large mortars, but none as large as the Mallet, were to be used with devastating effect in the American Civil War, the Russo-Turkish War of 1877/78 and the Russo-Japanese War of 1904/05.

                                         Mallet Mortar at Fort Nelson
Antoine Vanner provides a hint as to scale - and bombs in foreground are 36" diameter

                  Method of elevation can be seen - timber baulks used to change angle

Sebastopol was however to see deployment of giant mortars in a later siege. In 1942 German forces used self-propelled "Karl-Gerät" siege mortars to reduce the fortress. These monsters fired 24 inch shells of 4780 pounds maximum, and achieved a six-mile range with lighter 2,760 lb shells. Each weapon was by a crane, a heavy transport trailer, and several modified tanks to carry shells.


The two Mallet Mortars still exist. The weapon used for testing can be seen at Woolwich, SE London (junction of Repository and Hillreach Roads , easily visible on Google Earth street view), close to what was the arsenal there. The unfired mortar  is on display at the Royal Armouries Museum at Fort Nelson, just north of  near Portsmouth. The photographs were taken there recently.

                                                Karl-Gerat in action in WW2

Despite the failure of his mortar, Robert Mallet’s career continued to prosper. His detailed investigation of the 1857 Great Neapolitan Earthquake, which caused 11,000 deaths, produced a two-volume report,  subtitled “The First Principles of Observational Seismology" and in it he demonstrated that the earthquake had some eight to nine miles below the surface. Mallet was also to do pioneering work on volcanology. He was elected Fellow of the Royal Society in 1854, and moved to London in 1861. Highly honoured, it is sad to record that he was blind for the last seven years of his life. He is buried at West Norwood Cemetery – an Eminent Victorian who deserves to be remembered.

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