Life on the battlefield if very Hobbsian, rough, brutal, and short. While one avenue to pursue is improving armor and survivability to prolong a vehicle or soldier's combat effectiveness. The other avenue produced the Destroyer, ramping up the offensive power and accepting that the life span is effectively going to be short.
The Destroyer Pattern
Also known as a the 'Mammoth' or the 'Apocolypse' and a variety of other large and impressive words, the Destroyer Pattern is simple, mount two main cannons in the turret of a tank instead of one. The moves the targeting system between the barrels, and drastically reduces the amount of space inside the turret, as almost all the room available is used to house the cannons and their loading systems.
Increased Rate of Fire: With two cannons and two autoloaders, the Destroyer pattern tank can produce twice the number of shells downrange compared to the single cannon tank. One issue with large round autoloaders is that often the systems can be much slower than a manual operator feeding the gun, but by staggering fire, a steady stream can be produced even by tanks with less than optimal loaders.
Increased Weight of Fire: The Destroyer pattern can put two shells on one target with a twin linked targeting system. While a piece of armor might be able to resist a single hit, the force delivered by two can shatter or otherwise destroy said armor.
Intimidation Value: The visual image of large twin cannon tanks is intimidating, relating back to their impressive ability to wreak havoc and destruction on enemy forces.
Ammo Hungry: Destroyer pattern tanks obviously use ammo twice as fast as normal tanks, and require extensive logistics to keep them supplied with ammo.
High Priority Target: In a battle, the Destroyer Pattern tank is a primary target and is going to draw first response attacks, and if there are special armor busting assets in the area, they are going to divert to take out the Destroyer. This is not a good thing as the standard destroyer pattern tank is no more durable than a normal tank.
Destroyer Artillery: there is the potential to create destroyer pattern artillery pieces that twin mount long range guns in a single chassis. While it retains the advantage of increased rate of fire, it moves more artillery into a smaller area, which is a good and a bad thing. While it is safer from saturation attacks, compared to multiple scattered pieces, it is much more vulnerable to precision weaponry.
Destroyer Assault Guns: The assault gun is a tank with a front mounted cannon and no turret, and heavy armor. The Destroyer Assault Gun twin mounts cannons, but does so at the expense of the crew. The guns are buried in the hull with the crew members instead of in a turret, making the space cramped, and very loud when the guns are fired.
Energy Based Weapons: Laser and Plasma Destroyers can mount energy weapons rather than slug throwing cannons. These vehicles are involved in creating 'Beam Spam' attacks designed to overwhelm an opponent by sheer volume rather than a single heavy hit.
Magnetic Weapon Equipment: Destroyers can also in the right setting mount heavy coilguns, rail cannons, linear acclerators, or whatever the magnetic gun is called. These vehicles keep the same general profile as a conventional destroyer pattern just with longer range and typically higher accuracy.
The Destroyer Pattern Tank is going to be used in offensive roles, where it can bring down the thunder with it's big guns and deal large amounts of damage to defending units. It favors blitzkrieg, and ambush situations where it has the element of surprise or momentum on it's side.
In a Main Battle Role, the Destroyer is the core of an armored fist, supported by more conventional tanks. In a supporting role, the destroyer is armored cavalry, moving from hotspot to hotspot where it can dish out the pain where the pain is needed. In both of these roles, the tank is going to use strength in numbers to support it's high rate of attrition. In a defensive role, Destroyers are good choices for tank bunkers and fortifications designed to protect armored vehicles. It retains its impressive damage profile, and gains cover from return fire, and in a fortified position, it's general weaknesses can be mitigated by supporting units.
In the typical mecha environment, tanks are easy prey for the giant stompy robots. The Destroyer pattern tank is pretty guaranteed to get off at least two shots at an attacking mech before it is taken out, and as such can deal the same damage profile as two tanks. While it is easier to take out than two tanks, the cost of a second gun is a lot less than an entire second vehicle and second crew to man it.