Intermediate Armour - nrlulz/ACF GitHub Wiki
This tutorial continues from the principles in the Basic Armour tutorial. If you haven't read that first, you might miss some important context.
Basic continued: Ductility 101
The ACF Armour Tool lets you set the armour thickness precisely. It also contains another slider, for ductility. Ductility is a measure of the flexibility of an armour. Very flexible materials are ductile, and survive well under stress but offer very small levels of resistance to penetration. On the other side, very inflexible materials are liable to shatter under stress but offer very good protection against penetration. ACF uses the concepts of health and armour to model ductility. Ductile materials have large health values and small armour values. Fragile armour has very low health, but very high armour.
How to use ductility
The ductility slider in the ACF Armour Tool measures the ductility value in a range between -99 to 99. Negative numbers make the armour less ductile, and positive numbers makes the armour more ductile. At zero, the slider balances the armour ductility equally.
Fragile armour
Fragile armour is effective against all shells which rely on initial penetration to damage your vehicle. See the Shell Library for more information on which shells these are. This armour is very vulnerable to explosions. All shells which explode will quickly break fragile armour.
Ductile armour
Ductile armour will stop all shells which do not rely on penetration to do damage to your vehicle. See the Shell Library for more information on which shells these are. This armour is very ineffective against penetration. All shells which attempt to pierce will probably pass through ductile armour.
The danger of extremes (why 99/-99 will get you killed)
After learning about ductility, it sounds like a great idea to use fully fragile armour to make an impenetrable tank, or very ductile armour to roll out of explosions intact. This is a bad idea because your opponents frequently carry shells which can inflict both kinds of damage. Good armour is a balance between the two extremes: materials which can survive reasonable stresses and provide adequate armour value will protect a vehicle from the most common forms of harm. There are situations where combining biased armour can result in incredibly tough vehicle shells. This is called armour compositing and is an advanced technique. To learn more, visit the Advanced Armour guide
Thickness and bullet interaction
All armour has a thickness rating, measured in millimeters between the front surface and the back surface. This is commonly referred to as the RHA, or Rolled Homogeneous Armour value. RHA states the thickness of steel you would need to give the same protection as the armour you have, and makes a good metric for comparing different armours.
eRHA/sloping
Although RHA describes the relative thickness of armour between its two surfaces, it rarely describes the amount of armour a shell needs to pierce through to defeat the armour. When a shell hits armour at an angle, the distance between the point where the shell contacts the armour and the point where the shell exits the armour is longer than the RHA value. In tank combat, opponents are mostly on the same ground level and most shells will be fired parallel to the ground. If the tank's armour is sloped, then most of the shells aimed at it will hit it at the slope-angle and encounter the extra thickness provided by the slope. This thickness is called the armour's eRHA (effective RHA) and is a great way of getting extra armour protection from the same plate. Sloped armour is useful for more than just eRHA. If a shell is travelling fast enough and hits armour at a big angle, it will bounce off the armour harmlessly. These ricochets can be used externally to bounce shells away from the tank, or internally to redirect them away from vital components. To learn more, visit the Advanced Armour guide.
Pancake tanks
The extreme case of sloped armour is exhibited in "pancake tanks". These tanks use frontal armour with slope angles of 70-80 degrees from the upwards direction. When shells hit this armour, they frequently ricochet away from the tank and leave it unharmed. While pancake tanks have a huge advantage in that they avoid damage instead of absorbing it, they pay for it in reduced internal volume and increased frontal armour weight. Most pancake tanks have poor side and rear armour due to the extra weight required for the frontal armour which makes them vulnerable to flanking and indirect explosive fire. While pancake tanks are undoubtedly effective, they are controversial and many people dislike fighting them.
Layout concepts
Because ACF is part of a sandbox, you can build any kind of armoured vehicle you like. This section breaks down common types of vehicle and provides a guide to armouring them well.
Weight distribution
While knowing how to make good armour is important, knowing where to place it is more so. Most combat in ACF takes place in weight-classes, and this makes weight distribution important. Spending your weight budget in the right places makes the difference between a battle-scarred veteran and a smoking wreck.
Because tanks tend to engage targets from the front and remain still, tanks are heavily armoured on the front, with weaker armour on the sides and minimal armour on the back. Highly mobile vehicles may opt to have uniform armour values to achieve reasonable protection all around.
Tanks and Destroyers
Heavy tanks (HTs) are typically used in an assault role. Emphasis is placed on survivability over firepower. Because heavy tanks move slowly and turn more slowly, they are great targets for ambush. Heavy tanks should consider the possibility of taking fire from the sides, and allocate some armour there to survive ambushes while turning to face the threat. Heavy tanks are slow and lumbering, but reward the alert, aware player with great survivability.
Tank destroyers (TDs) are the opposites of heavy tanks. They focus on huge firepower instead of armour protection, and therefore rely on ambushes and long-range fire to remove the threat before it can fire back. Although they sacrifice most of their weight budget on their guns, their armour can take advantage of their tactics. A well-planned ambush will only take fire from its front, and so most of its armour should be placed there to take those hits. TDs reward smart and careful players with quick kills.
APCs and speed-tanking
APCs sacrifice armour thickness and firepower for raw speed. These vehicles outrun tanks, move quickly between cover to flank targets and avoid damage rather than taking it. Tank turrets usually traverse slowly (unless the tank is using an instant-turning E2, which is frowned upon in the community), which allows APCs to outrun the direction of the gun and attack from the rear. If a tank has already targeted an APC, it can also use its speed to avoid fire - there is a limit to a player's accuracy, especially when shooting at a moving target. Using speed to avoid damage is called speed-tanking.
Flank tanks
Flank tanks use lateral speed to defeat larger targets. A flank tank will allocate most of its armour to one of its sides, and then orbit its enemy with that side facing the target. The combination of speed-tanking and heavy armour results in a vehicle that can both avoid damage and take a few hits. This tank excels at 1 vs 1 combat, but can be easily flanked by a second enemy while engaging the first.
Watercraft
TODO: get someone who uses boats to fill this in.
Aircraft: bombers, fighters, orbiters
Aircraft battle in a more dynamic environment than tanks, and need different considerations when armoured. Dogfighters might choose to have the thickest armour at the rear of the aircraft, to protect against chasing aircraft. Bombers might choose to have heavy floors to protect from surface-to-air fire. Surface-attack planes will take the most fire when flying towards the target, so they may have thick frontal surfaces to absorb this fire. Aircraft which orbit the battlefield might choose to have heavily armoured sides: fire is less likely to come from the edges of the battlefield then the center of it.