The Breastplate Through History – Characteristics From the 14th Century Through the Present Day

This fully corroborates the earlier picture – that, though there’s an overall trend towards thickening, there are many examples of plates from 1580 and 1590 that are even thinner than breastplates from 1480 – which implies that there are essentially two trendlines:  Breastplates for cavalry got much thicker, whereas breastplates for infantry hardly changed or even grew thinner.

Now there are a few caveats to keep in mind.  First is that there might be more than a few tourney or parade breastplates hiding in both datasets, though I don’t believe this to be the case.  Second is that corrosion and cleaning/polishing both affect a steel or iron armor plate’s thickness – with corrosion thickening plates as the steel expands, and polishing thinning plates as material is removed – so we must assume that even the most meticulously drawn average has an error range of roughly ±0.25mm.  Third is that all breastplates were of uneven thickness, and they all varied to some extent.

On that note, it’s virtually always the case that the breastplate and helmet were the thickest parts of plate armor.  The edges and faulds of a breastplate were often much thinner, and arm and leg harnesses were generally thinnest of all, often under 1mm thick.  The thickness range for breastplates is 1.25mm to 7.8mm in all of the samples measured above – but the average gauntlet or fauld thickness might be well under 1mm.  

1. Breastplate areal density

There’s more information on the weights of breastplates than there is on their thickness, thickness being much more difficult to accurately measure.  Yet weight itself doesn’t tell us very much, as breastplates were made in a very wide variety of sizes and cuts, and some were of elaborate peascod designs.  We might benefit here from a degree of abstraction.

Low-carbon steel has a density of 7.85 gm/cc and iron has a density of 7.87 gm/cc – so close that they need not be considered separately.  Let’s take 7.86 gm/cc as an average value.

With that, we can construct a useful table of areal densities:

The average 14th-17th century breastplate has always covered roughly two square feet, or slightly under two square feet, in area. (Though, with few exceptions, they were made for shorter men than this era’s.  A 16th century design to fit a 6’ man would be somewhere over two square feet.)  For infantry, 10 pounds was considered the maximum usable weight, and this corresponds well to a thickness of just over 3mm.  A typical infantry breastplate would be around 8 pounds at a central average thickness of 2.5mm. The heaviest musket-proof cavalry breastplate would have weighed over 22 pounds, and at that weight would have been a real burden. 

III.  Breastplates, not backplates

In all of the above, we’ve only considered the weight and thickness of individual breastplates.  Backplates, throughout most of history, were very different: Thinner, lighter, and in some cases – especially in light cavalry and in the Austrian cuirassiers – not worn at all.  In the Allen collection, backplates appear to be generally around 50-65% the thickness and weight of breastplates, which seems like a pretty fair generalization.  It was not uncommon for an 8-pound breastplate to be paired with a 5-pound backplate.

In modern conflict soldiers are much more likely to be shot from the front – i.e. the bullet approaches from the front and impacts over the front of the body – and this was likely even more the case in the open-field conflicts of the 16th and 17th centuries.  As such, it would have been perfectly rational to wear a thicker breastplate and a thinner backplate – or no backplate at all.  (This applies particularly to mounted soldiers.  In infantry, it can be exceedingly uncomfortable to wear a breastplate, or a modern 10×12” armor plate, without a backplate.  Modern armor carriers and plate carriers generally match plates for this reason.)

1. The Cuirassier Breastplate

Though plate armor declined in popularity through the 17th century and was generally viewed as archaic and obsolete by the mid-18th, it did survive in the breastplates of heavy cavalrymen in Europe – the cuirassiers of France and their counterparts in other armies.  These breastplates were still in service at the outbreak of WWI.  Most 19th and early 20th century examples followed the 17th century tradition, with breastplates ~5-6mm thick, and much thinner backplates or no backplates at all.  What’s important to highlight is that these were never, as a general rule, 1mm-thick costume pieces – they were always functional, and arguably far thicker than they needed to be.

Today’s ceremonial cuirassier breastplates are generally antiques, or very closely modeled after antiques.  As far as can be ascertained, the final French cuirass is the so-called “3e republique” model which was produced from roughly 1870 until just after the outbreak of WWI – and they have not been modified since.  

The Italian Corazierri breastplate is much the same – it hasn’t been substantially modified since 1900, though there is a dedicated facility responsible for the cleaning and maintenance of those fine nickel-plated antique breastplates.  Though they’re quite functional and not exactly paper-thin, both the French and Italian models are used only for parade, ceremonial, and honor guard functions.

So the old European tradition of armor survives to this day, however in vestigial and much-reduced form.  Still, it’s nice, isn’t it?

1. Steel Body Armor in WWI

The steel body armor of WWI owes nothing to heavy cavalry cuirasses.  It followed the introduction of steel helmets over the course of that war, and was exhaustively chronicled by the Metropolitan Museum of Art’s arms and armor curator, Bashford Dean, in his 1922 book “Helmets and Body Armor in Modern Warfare.” 

To briefly summarize:

France was the first nation to issue steel helmets, and General Adrian – the man most responsible for those helmets, and after whom they are named – also recognized the high mortality abdominal wounds among soldiers, which prompted him to develop an abdominal armor plate.  In those days before antibiotics, abdominal wounds were apparently more fatal than chest wounds!

The abdomen plate, weighing two pounds, was held by a belt, though it was less favored by soldiers compared to the helmet. An attempt to add hip and groin guards was abandoned due to impracticality, but about 100,000 abdominal plates were produced and fielded.  Adrian also tested a five-and-a-half-pound breastplate and gorget that mounted to the abdominal plate, though the weight of this assembly prevented its widespread use. 

Later in the war, with both the abdominal plate and the breastplate abandoned, he produced steel epaulets – like scales – which were inserted into pockets in the uniforms of soldiers.  These were generally made from helmet trimmings, and provided some small measure of protection from shrapnel.

As with their helmets, the French body armor systems were generally very thin – on the order of 1mm or less – and were made from their low-carbon helmet steel.

The British experimented along different lines.  They produced a number of soft or “yielding” body armor systems from silk, linen, and other fabrics.  They also experimented with steel plates in fabric carriers – remarkably similar to modern steel plates in plate carriers.

An example below is the “Portobank armoured waistcoat.”