This is short primer on the difference between SP-Art, AG and TD.
Before we go further, let us first understand why SP-Art, AG and TD are not "tanks."
By a WWII-era "tank," we mean a gun-armed vehicle with the following features: (1) continuous tracks for all-terrain mobility; and (2) a rotating turret; and (3) overall armor protection.
SP-Art, AG and TD had (1) but lacked one or both of (2) and (3). Collectively, these three types can be called "self-propelled guns" instead of tanks.
Let us now distinguish among the different self-propelled guns.
The best way to understand the difference among these vehicles is the intended role of each.
I. SELF PROPELLED ARTILLERY
SP artillery is used in the indirect fire role, "standing off" and lobbing shots without directly engaging the enemy. Indirect fire has the advantage of being able to strike over obstacles at targets not directly in the line of sight.
Hence, SP Artillery is a howitzer mounted on a tracked vehicle. A howitzer projects shells on a parabolic trajectory. This gives the howitzer longer range, but less impact speed, and therefore less penetration. Therefore, howitzers usually have explosive shells, for use against soft targets at long range, like infantry concentrations.
As SP Artillery is not meant to closely engage the enemy, it usually has only light armor and is often open-topped.
Example:
Hummel (Germany)
Sexton (Britain)
M7 "Priest"(USA)
II. TANK DESTROYER
Tank destroyers are obviously intended as antitank weapons.
Hence, Tank destroyers are anti-tank guns mounted on tracked vehicles. An anti-tank gun fires a high-velocity hardened shell on a flat trajectory, for purposes of piercing through armor. This means that an anti-tank gun is not as effective against infantry concentrations and forts, as its shell would simply rip through the impact point with minimal blast.
The first German, Soviet and British tank destroyers were hasty lash-ups of existing towed anti-tank guns on any available tracked chassis, and hence had minimal armor.
While the US was not as hard-pressed as the other three nations in their anti-tank development, early US tank destroyers also had light armor. US planners believed that all-around armor protection against infantry and close-range fire was not necessary, since their TDs would only engage enemy tanks at long range, and enemy infantry would presumably be somewhere else being dealt with by the well-armored tanks. They belatedly learned that the enemy was not so cooperative.
In 1942-43 on the Eastern Front, the Soviets and Germans quickly realized that their open-topped improvised TDs were too vulnerable, and soon switched to purpose-built heavily armored TDs. Unfortunately, the British and Americans were not paying attention, and the early US tank destroyers received a nasty shock in the French hedgerows in '44.
However, the US and British did not emulate the Soviets and Germans in using heavily armored TDs. Instead, they dropped further research into TDs and simply up-gunned and up-armored their tank designs. The reason for the divergence in approach is probably cost - this is explained in more detail below.
Examples:
Marder II (Early German TD)
Elefant (Advanced German TD)
III. ASSAULT GUN
AGs are intended to give direct fire support to infantry against bunkers, buildings and other fixed targets impervious to infantry small arms.
This means two things: (i) as AGs closely engage the enemy, they need to be more heavily armored than SP Art; and (ii) since AGs are used to destroy fortifications and buildings, they need to have high-explosive shells, since an armor piercing shell, for example, would simply pass through a building without knocking it down.
Hence, AGs are guns mounted on tracked vehicles. The use of the term "gun" in contrast to "howitzer" is intended to indicate that the guns mounted on AGs have a flatter trajectory suitable for direct fire.
However while AGs were originally intended for direct-fire infantry support, it was soon discovered that they were effective against tanks as well. For example, while the explosive shells fired SU-152 "Beast Killer" could not penetrate Tiger and Panther armor, the blast was so powerful that it could simply blow off the enemy's turret. Also, some of the guns used on AGs were versatile enough to be fitted with proper armor-piercing shells, so that the AGs could be used as tank destroyers.
Examples:
SU-152 "Beast Killer" (Soviet)
Sturmpanzer IV "Brummbar" (German)
Why Not Just Build Tanks?
The US, Britain and Germany extensively used specialized self-propelled artillery. The Soviet Union did not have specialized self-propelled artillery, but they had assault guns that could perform indirect fire support (e.g. SU-76 and ISU-152).
However, the US and UK did not use assault guns at all. Also, they used open-topped tank destroyers only in the early stages of their armor development. When they belatedly realized that their open-topped TDs were too vulnerable, they did not go on to build the heavily-armored AG and TD behemoths that the Germans and Soviets so loved. Instead, they simply used up-gunned and up-armored tanks to fill the roles served by the German and Soviet casemate-style designs.
The reason for the divergence in armor development is simple: tanks may be superior overall, but AGs and TDs are much cheaper.
This is because AGs and TDs do not have the tank's complex rotating turret. Being simpler and cheaper, AGs and TDs can be built more quickly and in greater numbers.
The simpler construction also means that (i) they are usually more reliable, which means that less resources are consumed in repair and maintenance; and (ii) more armor can be piled on, as the simple design eliminates the weight of the turret's machinery.
This explains why Germany and the Soviet Union were the only nations to use these beasts on a large scale. These two nations were engaged in four years of desperate armored combat where hundreds of tanks were destroyed on almost daily basis. Fast, cheap production of reliable armor had a value on the Eastern Front far greater than it had in the West or the Pacific.
However, when economy is not such a vital consideration, tanks are overall the better choice. The rotating turret gives the tank an unmatched mobility and versatility.
This is why the US and Britain, with the luxury of mature, highly mobilized industries and longer production lines, and who never suffered tank losses on the scale experienced by the Eastern Front combatants, never felt an urgent need for heavily armored AGs and TDs. Instead, they simply produced enough tanks mounting different types of guns to fill the infantry support and antitank roles.
However, had the US and Britain experienced armored warfare on the scale of the Eastern Front, I think it likely that they would have taken AG and TD development more seriously.
This why I think that AoD is correct in allowing all powers, not just the nations that historically used them, to develop and use AGs and TDs. Then I can play out my fantasies of a British Tortoise desperately defending London in 1945 or a T28 assault gun destroying oncoming Kingtigers in the ruins of New York in 1949.
Simulating Tank Destroyers, Assault Guns and SP_Art in AoD
The early TD models would be represented by the lightly-armored TDs (e.g. Marder, Archer, M36 Jackson) and the advanced TD models would be the heavily armored monsters (Elefant, Jagdtiger, etc.).
The divergence in Ger/Sov and US/Brit TD development could then be explained in AoD game terms as Ger/Sov continuing research from the early to the advanced models, while US/Brit stopped researching the advanced TD models and focused on tank development. Of course, an AoD player would be free to follow a different path.
As for AGs, there is some confusion due to the fact that AGs were often used as tank hunters. Nonetheless, AGs such as the StuG III and the SU-152 "Beast Killer" were primarily designed as infantry support weapons and their guns were best suited for that role. The fact that they were widely used as a tank hunters simply reflects two things: (i) the AG's guns were versatile enough to effectively use AP shells, or they used hi-ex shells powerful enough to kill a tank crew from the sheer blast; and (ii) unavailability of purpose-built tank destroyers and tanks.
This can be modeled in AoD simply by doing the following:
1. making AGs cheaper to build than TDs.
(Historically, AGs were cheaper because howitzers are cheaper than anti-tank guns - that's why there were usually more AGs around than TDs. This also explains why they ended up being pressed into an anti-tank role - commanders scrounged desperately around for any available armor to stop tank assaults, and chanced upon the AGs much more than the scarce TDs.)
2. giving them good soft and hard attack values (reflecting the versatility of their guns).
3. The soft attack should be higher than the hard attack, to represent the intended purpose as an infantry support weapon. In comparison to the other mobile guns, the soft attack should be lower than SP_Art and the hard attack should be lower than TD. AG therefore represents a good low cost all-around weapon - which is historically why so many were built in the first place.
[Author's note: Credits to alant, Mjarr, Eugenioso and GAGA for providing additional insights which are incorporated in the revised version of this post.]
Implementation
1. Unit Stats
Simply change the appropriate values in db/units/brigades. The assault guns are in the file named b_u5.
2. Country-specific names and graphics
config/boostertext.csv has the following lines for generic assault guns:
BRIG_MODEL_35_0;Early Assault Gun;Canon d'assaut I;Cannone d'Assalto di base;Cañón de asalto básico;Einfaches Sturmgeschütz;Podstawowe Dzia³o Szturmowe;Arma de Assalto Básica;Áàçîâîå øòóðìîâîå îðóäèå;;;X
BRIG_MODEL_35_1;Basic Assault Gun;Canon d'assaut II;Cannone d'Assalto migliorato;Cañón de asalto mejorado;Verbessertes Sturmgeschütz;Ulepszone Dzia³o Szturmowe;Arma de Assalto Melhorada;Óëó÷ø. øòóðìîâîå îðóäèå;;;X
BRIG_MODEL_35_2;Improved Assault Gun;Canon d'assaut III;Cannone d'Assalto avanzato;Cañón de asalto avanzado;Fortgeschrittenes Sturmgeschütz;Zaawansowane Dzia³o Szturmowe;Arma de Assalto Avançada;Óñîâåðø. øòóðìîâîå îðóäèå;;;X
you can insert country-specific lines below that, for example:
BRIG_MODEL_GER_35_0;StuG III;;;;;;;;;;X
BRIG_MODEL_GER_35_1;StuH 42;;;;;;;;;;X
BRIG_MODEL_GER_35_2;Brummbar;;;;;;;;;;X
BRIG_MODEL_SOV_35_0;AT 1;;;;;;;;;;X
BRIG_MODEL_SOV_35_1;SU 152 'Beast Killer';;;;;;;;;;X
BRIG_MODEL_SOV_35_2;ISU 152;;;;;;;;;;X
The space before each semicolon represents a specific language. Just fill in the translated name at the appropriate point if you play in other languages.
In gfx/interface/models you can insert country-specific pictures as long as you name them correspondingly.
for example, for BRIG_MODEL_GER_35_0 you can insert a picture in gfx/interface/models of a StuG III (bmp and formatted to the same size as the other icon pictures) named as follows:
ill_bri_ger_35_0
Before we go further, let us first understand why SP-Art, AG and TD are not "tanks."
By a WWII-era "tank," we mean a gun-armed vehicle with the following features: (1) continuous tracks for all-terrain mobility; and (2) a rotating turret; and (3) overall armor protection.
SP-Art, AG and TD had (1) but lacked one or both of (2) and (3). Collectively, these three types can be called "self-propelled guns" instead of tanks.
Let us now distinguish among the different self-propelled guns.
The best way to understand the difference among these vehicles is the intended role of each.
I. SELF PROPELLED ARTILLERY
SP artillery is used in the indirect fire role, "standing off" and lobbing shots without directly engaging the enemy. Indirect fire has the advantage of being able to strike over obstacles at targets not directly in the line of sight.
Hence, SP Artillery is a howitzer mounted on a tracked vehicle. A howitzer projects shells on a parabolic trajectory. This gives the howitzer longer range, but less impact speed, and therefore less penetration. Therefore, howitzers usually have explosive shells, for use against soft targets at long range, like infantry concentrations.
As SP Artillery is not meant to closely engage the enemy, it usually has only light armor and is often open-topped.
Example:
Hummel (Germany)
Sexton (Britain)
M7 "Priest"(USA)
II. TANK DESTROYER
Tank destroyers are obviously intended as antitank weapons.
Hence, Tank destroyers are anti-tank guns mounted on tracked vehicles. An anti-tank gun fires a high-velocity hardened shell on a flat trajectory, for purposes of piercing through armor. This means that an anti-tank gun is not as effective against infantry concentrations and forts, as its shell would simply rip through the impact point with minimal blast.
The first German, Soviet and British tank destroyers were hasty lash-ups of existing towed anti-tank guns on any available tracked chassis, and hence had minimal armor.
While the US was not as hard-pressed as the other three nations in their anti-tank development, early US tank destroyers also had light armor. US planners believed that all-around armor protection against infantry and close-range fire was not necessary, since their TDs would only engage enemy tanks at long range, and enemy infantry would presumably be somewhere else being dealt with by the well-armored tanks. They belatedly learned that the enemy was not so cooperative.
In 1942-43 on the Eastern Front, the Soviets and Germans quickly realized that their open-topped improvised TDs were too vulnerable, and soon switched to purpose-built heavily armored TDs. Unfortunately, the British and Americans were not paying attention, and the early US tank destroyers received a nasty shock in the French hedgerows in '44.
However, the US and British did not emulate the Soviets and Germans in using heavily armored TDs. Instead, they dropped further research into TDs and simply up-gunned and up-armored their tank designs. The reason for the divergence in approach is probably cost - this is explained in more detail below.
Examples:
Marder II (Early German TD)
Elefant (Advanced German TD)
III. ASSAULT GUN
AGs are intended to give direct fire support to infantry against bunkers, buildings and other fixed targets impervious to infantry small arms.
This means two things: (i) as AGs closely engage the enemy, they need to be more heavily armored than SP Art; and (ii) since AGs are used to destroy fortifications and buildings, they need to have high-explosive shells, since an armor piercing shell, for example, would simply pass through a building without knocking it down.
Hence, AGs are guns mounted on tracked vehicles. The use of the term "gun" in contrast to "howitzer" is intended to indicate that the guns mounted on AGs have a flatter trajectory suitable for direct fire.
However while AGs were originally intended for direct-fire infantry support, it was soon discovered that they were effective against tanks as well. For example, while the explosive shells fired SU-152 "Beast Killer" could not penetrate Tiger and Panther armor, the blast was so powerful that it could simply blow off the enemy's turret. Also, some of the guns used on AGs were versatile enough to be fitted with proper armor-piercing shells, so that the AGs could be used as tank destroyers.
Examples:
SU-152 "Beast Killer" (Soviet)
Sturmpanzer IV "Brummbar" (German)
Why Not Just Build Tanks?
The US, Britain and Germany extensively used specialized self-propelled artillery. The Soviet Union did not have specialized self-propelled artillery, but they had assault guns that could perform indirect fire support (e.g. SU-76 and ISU-152).
However, the US and UK did not use assault guns at all. Also, they used open-topped tank destroyers only in the early stages of their armor development. When they belatedly realized that their open-topped TDs were too vulnerable, they did not go on to build the heavily-armored AG and TD behemoths that the Germans and Soviets so loved. Instead, they simply used up-gunned and up-armored tanks to fill the roles served by the German and Soviet casemate-style designs.
The reason for the divergence in armor development is simple: tanks may be superior overall, but AGs and TDs are much cheaper.
This is because AGs and TDs do not have the tank's complex rotating turret. Being simpler and cheaper, AGs and TDs can be built more quickly and in greater numbers.
The simpler construction also means that (i) they are usually more reliable, which means that less resources are consumed in repair and maintenance; and (ii) more armor can be piled on, as the simple design eliminates the weight of the turret's machinery.
This explains why Germany and the Soviet Union were the only nations to use these beasts on a large scale. These two nations were engaged in four years of desperate armored combat where hundreds of tanks were destroyed on almost daily basis. Fast, cheap production of reliable armor had a value on the Eastern Front far greater than it had in the West or the Pacific.
However, when economy is not such a vital consideration, tanks are overall the better choice. The rotating turret gives the tank an unmatched mobility and versatility.
This is why the US and Britain, with the luxury of mature, highly mobilized industries and longer production lines, and who never suffered tank losses on the scale experienced by the Eastern Front combatants, never felt an urgent need for heavily armored AGs and TDs. Instead, they simply produced enough tanks mounting different types of guns to fill the infantry support and antitank roles.
However, had the US and Britain experienced armored warfare on the scale of the Eastern Front, I think it likely that they would have taken AG and TD development more seriously.
This why I think that AoD is correct in allowing all powers, not just the nations that historically used them, to develop and use AGs and TDs. Then I can play out my fantasies of a British Tortoise desperately defending London in 1945 or a T28 assault gun destroying oncoming Kingtigers in the ruins of New York in 1949.
Simulating Tank Destroyers, Assault Guns and SP_Art in AoD
The early TD models would be represented by the lightly-armored TDs (e.g. Marder, Archer, M36 Jackson) and the advanced TD models would be the heavily armored monsters (Elefant, Jagdtiger, etc.).
The divergence in Ger/Sov and US/Brit TD development could then be explained in AoD game terms as Ger/Sov continuing research from the early to the advanced models, while US/Brit stopped researching the advanced TD models and focused on tank development. Of course, an AoD player would be free to follow a different path.
As for AGs, there is some confusion due to the fact that AGs were often used as tank hunters. Nonetheless, AGs such as the StuG III and the SU-152 "Beast Killer" were primarily designed as infantry support weapons and their guns were best suited for that role. The fact that they were widely used as a tank hunters simply reflects two things: (i) the AG's guns were versatile enough to effectively use AP shells, or they used hi-ex shells powerful enough to kill a tank crew from the sheer blast; and (ii) unavailability of purpose-built tank destroyers and tanks.
This can be modeled in AoD simply by doing the following:
1. making AGs cheaper to build than TDs.
(Historically, AGs were cheaper because howitzers are cheaper than anti-tank guns - that's why there were usually more AGs around than TDs. This also explains why they ended up being pressed into an anti-tank role - commanders scrounged desperately around for any available armor to stop tank assaults, and chanced upon the AGs much more than the scarce TDs.)
2. giving them good soft and hard attack values (reflecting the versatility of their guns).
3. The soft attack should be higher than the hard attack, to represent the intended purpose as an infantry support weapon. In comparison to the other mobile guns, the soft attack should be lower than SP_Art and the hard attack should be lower than TD. AG therefore represents a good low cost all-around weapon - which is historically why so many were built in the first place.
[Author's note: Credits to alant, Mjarr, Eugenioso and GAGA for providing additional insights which are incorporated in the revised version of this post.]
Implementation
1. Unit Stats
Simply change the appropriate values in db/units/brigades. The assault guns are in the file named b_u5.
2. Country-specific names and graphics
config/boostertext.csv has the following lines for generic assault guns:
BRIG_MODEL_35_0;Early Assault Gun;Canon d'assaut I;Cannone d'Assalto di base;Cañón de asalto básico;Einfaches Sturmgeschütz;Podstawowe Dzia³o Szturmowe;Arma de Assalto Básica;Áàçîâîå øòóðìîâîå îðóäèå;;;X
BRIG_MODEL_35_1;Basic Assault Gun;Canon d'assaut II;Cannone d'Assalto migliorato;Cañón de asalto mejorado;Verbessertes Sturmgeschütz;Ulepszone Dzia³o Szturmowe;Arma de Assalto Melhorada;Óëó÷ø. øòóðìîâîå îðóäèå;;;X
BRIG_MODEL_35_2;Improved Assault Gun;Canon d'assaut III;Cannone d'Assalto avanzato;Cañón de asalto avanzado;Fortgeschrittenes Sturmgeschütz;Zaawansowane Dzia³o Szturmowe;Arma de Assalto Avançada;Óñîâåðø. øòóðìîâîå îðóäèå;;;X
you can insert country-specific lines below that, for example:
BRIG_MODEL_GER_35_0;StuG III;;;;;;;;;;X
BRIG_MODEL_GER_35_1;StuH 42;;;;;;;;;;X
BRIG_MODEL_GER_35_2;Brummbar;;;;;;;;;;X
BRIG_MODEL_SOV_35_0;AT 1;;;;;;;;;;X
BRIG_MODEL_SOV_35_1;SU 152 'Beast Killer';;;;;;;;;;X
BRIG_MODEL_SOV_35_2;ISU 152;;;;;;;;;;X
The space before each semicolon represents a specific language. Just fill in the translated name at the appropriate point if you play in other languages.
In gfx/interface/models you can insert country-specific pictures as long as you name them correspondingly.
for example, for BRIG_MODEL_GER_35_0 you can insert a picture in gfx/interface/models of a StuG III (bmp and formatted to the same size as the other icon pictures) named as follows:
ill_bri_ger_35_0
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