From the moment at Agincourt when a single soldier was killed by a gunpowder weapon, armour protection became more and more impractical. The large scale of issue needed and the cost due to lack of manufacturing meant for most of history the best protection a soldier could wish for was a padded outfit.
This carried on into the first industrial war, World War One. In the early years of that war cloth caps were the norm, however with modern warfare modern mass production arrived and the benefits of metal helmets were realised and issued en-masse.
In the First World War several attempts at protecting the soldier from enemy fire were also tried, the best known was the German Lobster armour. However there were several other concepts tried.
MacAdam shovel in action, notice how the loophole is actually to low to the ground to be used without the mound of earth.
One was the ill-conceived MacAdam Shovel from Canada. It was designed, in 1913, to function as not only a shovel, but also as a bullet shield. The idea being that the soldier stuck the blade of the shovel into the ground, this gave him an armoured screen with a loop hole in it so he could fire at the enemy, while their return fire was deflected by the blade.
You can see how short the handle is on this picture.
To make it bullet proof it was built of very dense and heavy steel. However this was unable to stop enemy fire, and resulted in a very heavy shovel, with a short handle and a hole in the shovel blade.
In reality the shovels never made it closer to the front than England and were finally sold off as fifty tons of scrap at a massive loss to the Canadian Government.
Martel's one man tank. this is the MK2 version, made out of actual metal. the Prototype had been made of wood.
In-between the wars one British officer, Giffard Martel, came up with an idea for a one man tank. The idea is said to have come from a discussion with another British officer who witnessed a French tank attack during the First World War, and the swarm of FT-17's. When Martel pitched his idea it was laughed at, so he cannibalised an old car and rebuilt it at home in the shape of a one man tank. His plan was for each infantry unit to have a handful of these, and they would advance with the infantry giving covering fire. When the difficulties of one man doing all the jobs for the tank arose Martel countered by pointing to fighter pilots doing all the jobs required in their one man vehicles. Martel went one step further and proposed that every infantryman should be mounted in one of these tankettes.
Carden-Loyd one man tankette
As the idea was looked at other companies got in on the act, however the high point for the one man tank was the Dominion Premiers demonstration, in 1926. The army put several of its machines, including the A1E1 Independent through a demonstration.
Dominion Premiers demonstration in 1926
In less than a couple of years the idea had disappeared. However the one man tank does have one success story. Martel also built a two man version, and from this starting point you can trace a direct development through to the unparalleled success of the Universal Carrier. The idea of a slow moving tank to support the infantry in their advance could also be said to have resulted in the A11 Matilda Infantry Tank, however the link there is much more tenuous.

Soviet SN-42
In World War Two body armour made another appearance. The two best known are the Soviet armours like the SN-42, or the US flak jackets worn by bomber crews. A less well known version was a Japanese attempt at body armour, looking like a direct copy of the Soviet armour, it was let down by Japanese manufacturing, proving to be extremely heavy and offering no protection.
The British also worked on body armour. During the early 40's the Medical Research Council and the army thought through the problem, and eventually produced a usable armour.

The basic problem was that technology, at the time, couldn't provide armour thick enough to provide protection to prevent high velocity projectiles from penetrating the armour and causing damage. There were also certain places where low velocity projectiles would cause fatalities. Adding to the issue was that the Army had imposed a weight limit. The armour was designed to cover the most amount of vulnerable body parts within the constraints of the weight limit.
The Armour was found to be proof against rifle fire from 700 yards, pistols at 5 yards and Thompson Submachine gun fire at 100 yards.
The armour was mostly used by the RAF and 21st Army Group. There's anecdotal reports of it going ashore on D-Day and fighting through Normandy. It was definitely used during Operation Market Garden.
MRC armour can be seen on the soldier guarding these POW's.
After the war many ideas were tried for body armour, for both police and military uses, such as this police armour:
However its only due to modern technology that effective body armour has been realised.
My thanks to Volketten from the NA server, whom is a real expert in these matters and helped with this article.
Image Credits:
Milart, Wikipedia