A Fortress made to last: Science in action at the Redoubt

By Jay

Our upcoming science week here at the Redoubt Fortress has inspired us to look into some of the interesting features of the building and its armament that feature scientific application in their design. One such design is that of the impressive vaulted ceiling construction of the casemates themselves. A casemate is a room inside the walls of a fortress, and it was within these walls that the garrison ate, slept and worked.  They needed vaulted ceilings because of the sheer weight above them: the floor they support above them is actually the gun platform, which originally had to support the weight of ten 24-pounder cannon, and later cannon of the 32-pounder type!

The Oxford Dictionary states that a vault is a “roof in the form of an arch or a series of arches…”

However, the vaulted ceiling of the casemates we have here are not simply a series of arches to prop up the ceiling: the ceiling itself is a continuous run of brickwork extending from one end of the room to the other. Arguably it would be more accurate to consider the casemates as more akin to barrel vaults.

A barrel vault is a continuous arched shape, roughly semi-cylindrical in form, almost resembling some form of tunnel. We know that this type of design was used by the Romans in architecture, such as within the famous Colosseum in Rome. The vault needs to support the weight above it from around an opening, and a barrel vault can transfer this load, (the force bearing down upon the ceiling), across the entirety of the room, transferring it to the supporting walls either side. During construction, the bricks are usually mortared into position across a wooden- arch framework supported by interior scaffolding, which angles the bricks so as to make them “wedged in” against each other and gives the ceiling its characteristic curved shaped. This curved shape spreads the load from above down to the supporting walls, and so the entire room is able to support itself.

Gravity also plays its part in the design of the building. The latrines which were later built here on the gun platform are placed there so that there is some height from which waste and waste water can be flushed and drained away from the redoubt, all via gravity. The fortress also has stone guttering running around the edge of the entire gun platform, and again simply lets gravity feed the collected rainwater into underground water storage tanks. Simple…but effective! As the fortress sits on top of the beach shingle (which is perfect for drainage) and is above sea level,  excess water from rainfall or sea spray can drain away from the fortification via the dry moat and back down into the sea! Did you know the glacis (sloping earthworks surrounding a fortification) that originally surrounded the outer wall of the dry moat was also filled with shingle too?

The stone guttering here runs all around the inner edge of the gun platform. Its purpose was to collect rain water, some of which would filter down into the water storage tanks right here in the Redoubt. Useful for holding out during a siege!

There is one other aspect of scientific application we have time for! The Redoubt Fortress was a bastion of firepower in its day, supporting the series of nearby deadly Martello Towers, themselves surviving relics of the Napoleonic Wars (as is the Redoubt itself!). This was the age of the musket, the smoothbore cannon and of the sailing fighting ship! They all shared something in common: the volatile compound that was gunpowder!

Musketeers would complain of a gradual, unquenchable thirst for water the more they bit into prepared cartridges of gunpowder to arm their weapons, which would also stain their lips. Entire battlefields and gun decks on ships would reek of a smell similar to rotten eggs. Entire armies and ships of the line were often swallowed up in thick smoke during prolonged exchanges of gunfire…what was actually IN this gunpowder??

Gunpowder of the era was a black-coloured powder consisting three component parts: charcoal (which give it a natural black colour) to provide the burning chemical reaction with carbon and acts as a source of fuel, sulphur which serves as both a fuel and lowers the temperature needed for ignition, and potassium nitrate (commonly known as “saltpetre”) which supplies oxygen for the reaction. Its history stretches far back greater than this blog can cover, but by our era concerned, its explosive nature when ignited made it an effective chemical propellant for a wide range of projectiles. It was extensively used in weapons such as the musket and cannon. Once ignited by a heat source, it burns violently and produces gas in the process (approximately 40 percent of the end product from the reaction).

Sacks such as these would have been filled with gunpowder!

This particular type was used as the charge for cannon.

Its highly explosive nature meant that the hundreds of barrels of

gunpowder stored here at the Redoubt caused Eastbourne

residents some serious concern!

When confined in a tight space (such as the end of a musket barrel or cannon), sheer build up in pressure from this gas is sufficient to launch a projectile through an opening (such as the muzzle of a gun). The remaining 60 percent end product is mostly solids, contributing to the excessive amount of white smoke produced. The smell of rotten egg, you can probably guess, stems from the sulphuric byproduct! Typical mixtures for gunpowder consisted of somewhere around 75 percent saltpetre, 15 percent charcoal and 10 percent sulphur. However this was just a general rule of thumb: with minor changes in ratios, mixtures could (and did) vary through the ages and between countries.

There is still much more to be said on historical gunpowders and the science behind their composition, but perhaps that can be discussed another time!

That’s all from this month’s blog! See you next time!