Dale Fort Blog Number 57

15 03 2018

In which we discuss developments in mid 19th Century weaponry and what happened as a result at Dale Fort.

This article continues the story of the weaponry installed at Dale Fort, detailing the changes wrought in order to cope with the rapidly advancing military technology of mid to late 19th Century.

 Mid-19th Century Weaponry

The development of artillery at this time is complicated due both to rapid technological developments and changes in the philosophy of those responsible for defence policy.

Up until the mid-nineteenth century most guns had been smooth bored and muzzle loaded, firing spherical shot.

68lb coastal defence gun

Rifled barrels and Breech Loading

In 1854, Armstrong demonstrated his rifled breech-loader, which fired an elongated spinning missile.  A rifled barrel has spiral grooves cut into it.  The projectile engages with the grooves as it travels up the barrel and thus has spin imparted to it.  Spinning bullets and shells have better stability in flight and better accuracy and penetration.  By 1858 the British armed forces had decided to convert to these modern weapons.

RBL Armstrong gun labelled

There were several advantages:

Firstly, as mentioned above, the spinning projectile gave a degree of accuracy not seen with smooth bore guns.

Secondly, they were constructed from wrought iron. Previously, guns had been cast from iron or bronze.  As a result weak spots that developed did not become evident, except catastrophically when the barrel exploded in use.  Wrought iron gun barrels bulged before failing.

Thirdly, since the projectile was no longer spherical, its size and weight could be varied according to how much death and destruction you wished to wreak.

rifled barrel labelled

Dale and the rest of the 1852 Milford forts were not issued with  the first Armstrong guns.  The armed forces already possessed large numbers of RML 68-pounders.  The earlier weapons were simpler in construction, strong and cheap.  Armstrong guns were issued to mobile artillery and the Navy.  Static defences were considered to be armed adequately with the older equipment.

Ironclad Ships

    Around the time of the construction of Dale Fort, naval architects were experimenting with protecting ships from cannon fire by covering them with iron plates.  The French Navy was quicker off the mark than the British when it came to iron cladding its ships.  They also introduced steam powered ships earlier and it rapidly became evident that these were much handier, faster, more manoeuvrable and deadlier than sailing ships.

The launch of the steam powered La Gloire the first French iron clad, caused much alarm and despondency in the British press and among politicians.  Many felt that it rendered the British fleet impotent (about as much use as an aircraft carrier without any aircraft one might think).

La Gloire labelled

It was found by experiment that the new Armstrong breech-loaders were not up to the job of penetrating armour plated ships.  If the power of the charge in the guns was increased to try to make the shells more penetrative there was a tendency for the seal at the breech (a copper ring) to leak.  The system then became unreliable and dangerous by jamming or by the projectile exploding before it left the barrel.

A Retrograde Step?

The next step therefore was the seemingly retrograde one of reverting to muzzle loading guns which had a solid breech.  The advantages of rifled barrels and of firing an elongated missile were too great to give up and so the new muzzle-loaders were rifled.

The inside of the barrel had three deep spiral grooves cut into it.  These grooves engaged with rows of studs around the body of the projectile.

stuuded shell labelled

The charge was placed in the barrel, rammed down and a gas check plate made of soft metal put on top.  The studs on the missile engaged with the grooves at the top of the barrel and the shell twisted down to sit on top of the charge.  When the charge exploded, the gas-check plate melted and formed a seal.  The missile would be forced up the barrel, twisting up the grooves as it went and would be spinning as it left the muzzle.  These guns were called rifled muzzle-loaders (RMLs).  Later versions had the gas check plate incorporated into the base of the shell, which was no longer studded.  The plate melted and engaged with rifling in the barrel eliminating the need for studs.

These developments rendered obsolete the many old smooth bore muzzleloaders already in service at places like Dale Fort.  The solution came from Captain Palliser, who devised a method for converting the old smooth bore muzzleloaders into rifled guns.

The old barrel was bored out to remove erosion marks and a wrought iron rifled liner slid into place.  A heavy charge was fired from the gun and this served to expand the liner into the old barrel.  It was found that these converted guns were actually stronger than the originals and so could fire a more powerful charge.  More than 2000 conversions were carried out and that included the guns at Dale.

What sort of shell was best?

There were two schools of thought on the nature of the projectile that should be fired from these RMLs.  One group favoured a large slow moving projectile the aim of which was the total destruction of the ship it was fired at.  The intention was to shake the whole structure to pieces.

The other school favoured a lighter, faster projectile aiming to penetrate the hull of the ship and wreak havoc from the inside.  After many trials, it was discovered that the most important thing, if you wanted to penetrate armour plating (which could be 5 inches of iron backed by 2 feet of oak), was to maximize the speed at which the missile hit the plate.  This gave the material little time to spread the impact by deforming elastically.  Speed was more important than mass.

Penetration could also be improved dramatically by hardening the tip of the shell.  Palliser invented the means of doing this by quench cooling the point of the shell during manufacture and letting the rest of it cool slowly.  Palliser shot became the standard armour piercing ammunition for years to come.

Palliser shell labelled

Look out for Blog 58 which might be more biology based (on the other hand, I just might tell you about The Zalinski Pneumatic Dynamite Torpedo Gun).

 

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