I think the current goal is 225 tanks in the future army, which really isn't that much, actually.
So then, were are we going with a more deployable expeditionary / medium tank at around 40-45t, TerraN?
Kinetic protection against 30mm rounds of all kinds from the front and at least 14,5mm all around, with cage armor add on also against basic RPG-7 types.
And then, to be usefull in higher intensity scenarios, all around protection against RPG-29V type and basic ATGMs via an APS with soft/hard-kill means?
Besides a 120 main gun I would propose a gun launched ATGM to out-range heavy IFVs other tanks. Or anything with intermediate caliber guns. And also some kind of automated small mortar, large GMG to subdue infantry threats and provide a safty buble for the vehicle.
All of that is going to be quite expensive. To the point were it pulls the whole conceot into question. For the wide range of operations were heavy combat vehicles aren't a real concern, but were a solid punch is still required against structures and light vehicles, I'm sometime thinking HESH rounds. Though these would need a rifled gun, unless their guided themselves, wich would drive up cost even more.
Not every nation is going to adopt lighter tanks some are going to feel the need to maintain heavier tanks the Altay and K2 for example. South Korea feels the need of heavy MBT's as North Korea has something like 3-4x the number of MBT's mind you the North Korean MBT's are dated at best primarily T55's, Type 59's, T62's, T62 clones and A T62/T72/T90 hybrid but numbers count for something.
the Question Comes down to needs. for the US Who needs to move it's forces to the fight or Japan who more and more are facing tensions along there outer perimeter islands. are prime cases as is France and perhaps the UK. This I think will lead that any new tank and or IFV from these nation will need good protection but lighter weight well there existing MBT's will likely remain in service but at reduced numbers.
now in terms of protection remember the american M8 AGS back in the late 80's early 90's offered protection against 30mm cannon fire across the frontal arc in a 24.75 tons package. so a 35-45 ton tank could do alot better. one of the factors I see is that the Armor of the Tank and IFV and APC is becoming tailored. more and more the tank can grow lighter by moving the extra protection to "Bolt on" tiles. over all armor of future vehicle is becoming a less a built in and more a bolt on.
Along with Plates Cage or Slat armor will be a feature kept but some things to keep in mind.
1) Slat armor is nothing new or cutting edge the first generation was used by the Germans in WW2 in reaction to Hollow Charge weapons used by the Allies. Tandem Charge warheads for RPG's can work around the Era or Slat.
2) RPG's are common but dated more and more ATGM's are moving to the fore front, Look at Syria and Iraq where Groups whether AQ, ISIS,other islamist and non-islamist are widely using ATGM's widely. and many are top attack which is unprotected by ERA or Slat.
3) Slat although comparatively light weight takes up space due to stand off space needed for it's operation a Stryker ICV with slat cannot be loaded on a C130J it has to be Shipped with it unattached and then mounted on site.
This may push more for a "Comprehensive" approach combining Aplaques, Era, Slat and a APS Strategically over the vehicle. placing Slat over Engine exhaust and optics, Aplaques and Era over critical points on the hull and a integrated Soft and hard kill APS options. This will not be cheap but smarter in the long run as each system can be replaced and updated as needed mush easier then just the integrated armor of a tank. another feature that seems to be coming into vogue is remote or Unmanned Turrets. This offers a nice option for a number of reasons. by making the Turret unmanned in the event of a top attack ATGM the Turret my be disabled but the Crew is in the Hull this means you only really have to focus on armoring the hull as that's where all the most valuable mission needs are. The Human crew. this also means that the Driver, Commander Gunner and any other crew can share the Same NBC protection as opposed to needing a separate set for the driver vs the Turret.
Additionally I am thinking that more and more we are going to see Tanks and armored vehicles try and counter detection. as is simple RAM coatings and Thermal Mitigation techniques are already being integrated onto armor and Concepts like the Hybrid drive from BAE mean the vehicle can be more efficient, use smaller engines placed in smaller off center locations allowing more space in the hull for ammo, personal and gear. this can also mean easier conversion to a IFV.
speaking of which an ATGM from a Autocannon would demand a large calibre gun at least a 50mm like the ATOM IFV's 57mm that's going to be heavy take up space because of not just the cannon but a munitions system that can change from conventional AP, HE, to your guided rounds and weight for storing such. that''s not to say it's impossible the Russians BMP1 and BMP3 do it but with low velocity cannons the 73mm 2A28 Grom on the BMP1 and the 2A70 100mm rifled gun on the BMP3. mostly though I think the IFV standard will stay between 25-40mm autocannons with a number of Antitank Guided missiles in some form of launcher.
Within the next decade we will be seeing rail gun technology adopted into main guns of MTB since the gas turbine generators can generate more than sufficient amount of electricity to power the guns.
With these guns armor will become less relevant since no matter how thick you make them the rail guns will rip right through it.
I agree, but there is still one question I have. Tank Guns are not just used for Armor Piercing rounds. they are also used for guided missiles, Anti Personnel canister rounds and high explosive shells which still have to be proven on a railgun. there are also going to be conventional guns for some time and possibly alternative gun technologies. Coil guns are said to be being looked at for Mortar systems by DARPA. a ram accelerator round might equalize a conventional to rail gun battle. so could a combustion light-gas gun or a scram cannon or electrothermal-chemical technologies which could be more of a hybrid.
