Throughout the last few years I've seen a great many projects related to armoured warfare. Nearly every single one of them was scuppered by technological considerations. Either the technology was unavailable, or too cutting edge and so would cost too much. However with modern technology these ideas suddenly become feasible, in most cases tanks continue to be churned out looking much like the FT-17. So, let's consider some of the past projects and how they can fit in current warfare.

You might not know it, but there are laws to tank design. Break them and your tank will fail.This law is simple that there is a ratio of a tank's footprint, i.e. the surface of the track in contact with the ground, the track gauge. Both of these factors have an impact on the tanks width and length, lest you end up with something like a St Chamond from the First World War.
This is because as a tank gets longer it gets harder to steer, as there's more track in contact with the ground. If you consider the tanks centre as a pivot point, and two parallel lines as the tracks in contact with the ground, then the edges of the tracks have the furthest to travel, equally they have the most resistance to overcome. As you make the length longer, you increase the footprint in contact with the ground, and thus the forces involved. Make a tank too short and it'll not be able to cross trenches, and it will lack stability. So you have to balance these requirements. The ideal ratio is about 1.3-1.8 times the width of the tank.

Now the length and width from the base of the tank also affect how high you can take the centre of gravity, take it too high and your tank will start to flip over. From this you can see that all three dimensions on a tank are related to each other.

Early tanks had a further trouble as they used skid steering. This is where one track is locked and the other drives dragging the tank around, this adds a massive anchor to one side of the tank. In Rhomboids of the first World War it was made worse by the two large gun sponsons right over the tracks. Another tank that broke this rule was the T-35. The engine used in the T-35 was the Mikulin M-17. This was also used in BT series and T-28's. While the latter two were not considered super reliable, they were vastly better than the T-35. The T-35 had between 49-51 units issued, in its combat tour in 1941 only five were lost to enemy action but 43 were lost due to mechanical breakdown. A large portion of those would be due to the over taxed engine just giving up.
Even today the ratio causes problems. The newest British IFV the Ajax has been accused by some commentators as being too long and too wide. This is a factor of the need to have enough length to fit infantry dismounts in the back.
However by the 30's engineers were beginning to look at solving this issue, although they didn't know it. Giffard Le Quesne Martel, a famous British Army engineer officer that pioneered the use of tanks and bridging equipment, and who commanded the British at the Battle of Arras was in India and started looking at the problem. It was known that smaller tracked vehicles such as the Carden Loyd MG carrier steered just fine, but even the next step up, the light tank caused steering problems until a specialist gearbox was developed. But even then there was a theoretical maximum length to the light tank. He began to look at ways to make steering easier by making the tanks actually turn, like a truck, instead of skid steering.
His idea was to have four sets of tracks, two at the front and two at the rear. This four track set up has massive advantages in tank design. First it's much more stable, for example a bump or boulder would simply fit inside the gap in the tracks, where as a tank of the same length would still be rearing up until it tipped over. The tank would steer like a truck, which would make crew training a little bit easier. It also adds a bit of survivability to the tank, meaning it could theoretically continue to maintain some degree of mobility after a track was destroyed by a mine hit. Most importantly it disconnects the ratio of length vs width. In the case of an armoured vehicle carrying infantry it'd also give a useful position to mount a set of dismount doors in the side hull.
On these two images note where the doors hinges are located. This means they open out one each way, so that no matter which direction enemy fire is coming from you have an armoured door covering you as you dismount. Possibly a good idea for these side doors on the four track IFV?
In the last 40 years there have been at least two serious suggestions (that I know of) to make AFV's with four tracks. However these have all been shot down by more traditional officers who consider the idea too new fangled and too technical. But consider this. Martels prototype was hand built by himself in a shed at home, with 1930's technology. That was a tank with all four tracks driven mechanically, and it worked. Hägglunds has been producing four track articulated all terrain vehicles, such as the BV-206, that have seen wide service throughout European militaries.
In fact the concept of four tracks is actually easier now than it ever was, with the advent of hybrid electric drives you no longer need to run mechanical power to the track units, making maintenance and reliability even better. So maybe it's time to look at four track tanks again?

Another thing one sees a lot of in the 1980's is elevating ATGM platforms. Such as this German entry.
The arm erects to launch ATGM's across the battlefield, while the launching tank stays nice and safe.

Now the two main driving forces behind its cancellation was the end of the Cold War, and the massive elevating arm. That's a lot of weight in an AFV, and it also takes time to erect and the vehicle can’t move if it’s erected. However in the 1960's as part of the infamous Project Prodigal some bright chap suggested drones connected by radio to a tank to attack enemy targets. His sketch shows tiny helicopters linked to Centurions, flying above the tank platoon as it charges towards Soviet armour, the mini-helicopters are adding their fire-power to that of the Centurions resulting in a total rout of the enemy defences.
But what if we combine the two ideas? Quadcopters are getting pretty advanced, to the extent the average person can buy one cheaply. And look at Amazon's latest idea, drones delivering parcels. Beef the engines up a bit, and get them to carry a single ATGM. You get all the advantages of the arm mounted ATGM, without the negatives. You could for example have one of these drones lurking inside a building, where you'd not normally be able to mount ATGM's due to the problems of backblast. Or you could use a drone for reconnaissance, like a forward observation post, or similar roles such as ISTAR.

Another old British idea, that oh so nearly became reality that could help the modern British military, is that of liquid propellant. In the late 1950's and 1960's the British started studying liquid propellant. They even converted a couple of guns to test fire them. The main problem was that of uneven ignition of the propellant, which in turn gave wildly different muzzle velocities. If the issue of uneven ignition could be fixed then it could solve a huge issue facing the British Army.
At current our Challenger 2 tanks are getting old, and we can't replace the gun. To do so would mean ripping out the ammunition storage and that would pretty much require an entirely new tank, or at the very least an entirely new turret. The main driving force behind this is that tank penetrators have gotten longer to provide more penetrating power. Of course a longer penetrator is subject to more yaw force, which means it breaks up easier, but the general consensus from those in the know whom I trust is that the longer penetrator is better.
The current gun on the Challenger 2, called the L30, uses bag charges. On modern guns the penetrator extends down into the case of the round, which is something you cannot do with an L30.
So you have the issue of what to do. Well consider a new breech with more chamber space and a longer penetrator. Then consider a liquid propellant. The restrictions of the bag charge are removed, you could even create tanks to store the charge liquid in the same size and shape of the current charge bins, and the rod could be as long as is needed.
Charge bins in a Chieftian
You might even get advantages such as a higher rate of fire, or open the way for larger shells. As one big technical issue that people are bumping into is the next logical step up in tank calibre is to the 140mm. But the shells become so large you're limited to the number you can carry and hand loading is all but impossible.
When in the 80's it looked like the main tank gun calibre was to be 140mm, this is the autoloader the British developed.
When reading the above, however, the thing to consider is I'm no engineer. I'm a historian. So there could be massive technical problems, especially in the last idea, which mean the suggestions won't work in the real world. So please treat this article as just a set of casual observations.

My thanks to Maddest, for his help with this.

Image Credits:,,