Bomber experience
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Ghpstage
Deity
General Tso
Panzer General
All combat units including bombers gain experience in my mod. 
Unfortunately the mod is in Alpha testing, so it's not totally playable as a game right now.
Unfortunately the mod is in Alpha testing, so it's not totally playable as a game right now.
Liquidated
Goofed Up on Cough Syrup!
Bombers and transports are the primary units you want to push out of towns with the highest initial xp, seeing as it's almost impossible for either to gain more.
For transports in Vanilla, I reserved Heroic Epic + Westpoint in the highest hammer town that was coastal, just to aim for 10xp (flank, nav1, nav2) so they could keep up with stock speed dessies. Assuming warlords was just a bad dream, BTS brought settled GG's and theo (and the pentagon!) to make getting 10xp units out the door a rather trivial matter. Sad that I seldom bother with west point anymore if no stone around.
For bombers, I invariably end up spitting them out of those captured capitals the AI stuck 4 gg's in
; I seldom use bombers unless there is transcontinental warfare involved. I don't use the IW town because I always end up sticking red cross in that town. Innate medic means march is one promo away for arty or paratroopers, too nice to waste pushing out bombers.
Cheers!
-Liq
For transports in Vanilla, I reserved Heroic Epic + Westpoint in the highest hammer town that was coastal, just to aim for 10xp (flank, nav1, nav2) so they could keep up with stock speed dessies. Assuming warlords was just a bad dream, BTS brought settled GG's and theo (and the pentagon!) to make getting 10xp units out the door a rather trivial matter. Sad that I seldom bother with west point anymore if no stone around.
For bombers, I invariably end up spitting them out of those captured capitals the AI stuck 4 gg's in
; I seldom use bombers unless there is transcontinental warfare involved. I don't use the IW town because I always end up sticking red cross in that town. Innate medic means march is one promo away for arty or paratroopers, too nice to waste pushing out bombers. Cheers!
-Liq
TheDS
Regular Riot
I'm pretty sure Bombers can kill fighters defensively, right? Don't they gain XP for that? Otherwise, I guess you should build your bombers at an Airport with West Point and be in Vassalage and Theocracy (with the appropriate religion in that city). Should get you 3 promos. Pop a GG in there and he gets another promo. Pentagon can replace one Civic.
s.bernbaum
Mostly lurking
Bombers don't kill fighters. Either they evade the fighter and complete the mission or they get shot up, thereby taking damage and returning home without completing the mission, or getting destroyed.
God-Emperor
Deity
It is possible for a bomber to shoot down the fighter in an interception, but only if the fighter has at least 50% damage when the interception happens.
The combat during an interception works via rounds the same as any other combat in the game with the main difference being that there is an upper limit to the number of rounds of combat that can happen (5 in unmoded BtS) which is why both units can survive without there being a withdrawal chance. The odds of winning each round is proportional to the units' air strength values. Given that an undamaged BtS Bomber has an air strength of 16 and the undamaged fighter has a 12 the bomber has a 16*100/(16+12) percent chance of winning each round, which is actually 57% (since it is rounded down). That makes it look like the bomber should win the fight more than the fighter. But that does not take into account the amount of damage that is inflicted when a round is won. The damage inflicted is calculated as a defined value, MAX_INTERCEPTION_DAMAGE which is normally set to 50, scaled by the unit's current interception chance. A fighter has an interception chance of 100 so it will inflict 50 points of damage when it wins if it is undamaged. A Bomber has an interception chance of 0 so it looks like it will not do any damage, but there is also a defined MIN_INTERCEPTION_DAMAGE which is set to 10 so a bomber will do 10. At this point it is important to note that a unit's interception chance scales with the damage it has taken - if the fighter has taken half damage then it will have half the interception chance and also do half as much damage when it wins a round.
So with an undamaged bomber (no promotions) vs an undamaged fighter (no promotions) the bomber will win, on average, 57% of the combat rounds with up to 5 rounds before the fight ends. It only takes the fighter 2 hits, gotten by winning 2 rounds, to shoot down the bomber but it would take the bomber 10 hits to shoot down the fighter (which is not possible because there are only 5 rounds). That 57% chance per round for the bomber means the fighter often takes some damage and it is also why it is possible for the bomber to survive - it has to win at least 4 of the 5 rounds of combat to do so, working out to about a 28.7% chance of surviving. There is about a 6% chance that the bomber will win all 5 rounds and take no damage itself while causing the fighter 50 points of damage.
An undamaged bomber vs. a half damaged fighter is the point where it becomes possible for the bomber to shoot down the fighter - even a single hit point more than half left for the fighter means it can't happen. If neither unit has any promotions, the bomber now wins 16*100/(16+6) = 72% of the combat rounds (since the air combat strength of a unit scales directly with damage, the half damaged fighter is only strength 6 instead of 12). It now will take the fighter 4 hits to shoot down the bomber (as it will cause 25 points of damage per win) and it will take the bomber 5 hits to shoot down the fighter. If I did the math right, there is about a 98% chance that the bomber will survive and about a 20% chance that it will shoot the fighter down. (And there was only a 50% chance that the fight would even happen, the other 50% of the time the bomber is not intercepted and gets to perform its assigned mission.)
There is a condition in the code that does allow a bomber to get experience without shooting down the intercepting fighter. It is the condition where both units survive and not only did the bomber survive but it took no damage, which requires winning all 5 combat rounds when the fighter has at least 51 hit points at the start. That has about a 6% chance of that happening for the usual no damage no promotions example. When it does happen, the bomber gets the number of XP specified by the EXPERIENCE_FROM_WITHDRAWL setting, which is 1 for BtS. If both units survive but the bomber takes damage, then the fighters gets this experience unless the fighter took no damage (which can only happen if the fighter started out damaged badly enough that it can't destroy the bomber even when it wins all 5 rounds, but the odds of it winning all 5 when it is so badly damaged are very low - I expect this is in there for ground units that can intercept since they never take any damage when intercepting so they will always trigger this exception).
All this is why you should clear the way with fighters first. Assuming equal promotions, it's pretty much a 50-50 fight for 2 undamaged unpromoted fighters. There is no chance that both will survive since they each need 2 hits to destroy the other and there is no way for that to not happen when the round limit is set to 5 (it would have to be way down at 2 for this to be possible). So either you eliminate a defending fighter (with a 50% chance of your fighter being undamaged and a 50% chance of being half damaged) or you don't but have a 50% chance the defender is at half damage. That is a lot better than the roughly 71.3% chance that an undamaged unpromoted fighter will shoot down an undamaged unpromoted bomber (and a 100% chance that it will intercept, preventing the bomber from doing what it was trying to do). Starting by sending in cheaper unit with a better survival chance = a good plan.
Some of the odds calculations might be slightly off, but I think this is all correct. Probably.
The combat during an interception works via rounds the same as any other combat in the game with the main difference being that there is an upper limit to the number of rounds of combat that can happen (5 in unmoded BtS) which is why both units can survive without there being a withdrawal chance. The odds of winning each round is proportional to the units' air strength values. Given that an undamaged BtS Bomber has an air strength of 16 and the undamaged fighter has a 12 the bomber has a 16*100/(16+12) percent chance of winning each round, which is actually 57% (since it is rounded down). That makes it look like the bomber should win the fight more than the fighter. But that does not take into account the amount of damage that is inflicted when a round is won. The damage inflicted is calculated as a defined value, MAX_INTERCEPTION_DAMAGE which is normally set to 50, scaled by the unit's current interception chance. A fighter has an interception chance of 100 so it will inflict 50 points of damage when it wins if it is undamaged. A Bomber has an interception chance of 0 so it looks like it will not do any damage, but there is also a defined MIN_INTERCEPTION_DAMAGE which is set to 10 so a bomber will do 10. At this point it is important to note that a unit's interception chance scales with the damage it has taken - if the fighter has taken half damage then it will have half the interception chance and also do half as much damage when it wins a round.
So with an undamaged bomber (no promotions) vs an undamaged fighter (no promotions) the bomber will win, on average, 57% of the combat rounds with up to 5 rounds before the fight ends. It only takes the fighter 2 hits, gotten by winning 2 rounds, to shoot down the bomber but it would take the bomber 10 hits to shoot down the fighter (which is not possible because there are only 5 rounds). That 57% chance per round for the bomber means the fighter often takes some damage and it is also why it is possible for the bomber to survive - it has to win at least 4 of the 5 rounds of combat to do so, working out to about a 28.7% chance of surviving. There is about a 6% chance that the bomber will win all 5 rounds and take no damage itself while causing the fighter 50 points of damage.
An undamaged bomber vs. a half damaged fighter is the point where it becomes possible for the bomber to shoot down the fighter - even a single hit point more than half left for the fighter means it can't happen. If neither unit has any promotions, the bomber now wins 16*100/(16+6) = 72% of the combat rounds (since the air combat strength of a unit scales directly with damage, the half damaged fighter is only strength 6 instead of 12). It now will take the fighter 4 hits to shoot down the bomber (as it will cause 25 points of damage per win) and it will take the bomber 5 hits to shoot down the fighter. If I did the math right, there is about a 98% chance that the bomber will survive and about a 20% chance that it will shoot the fighter down. (And there was only a 50% chance that the fight would even happen, the other 50% of the time the bomber is not intercepted and gets to perform its assigned mission.)
There is a condition in the code that does allow a bomber to get experience without shooting down the intercepting fighter. It is the condition where both units survive and not only did the bomber survive but it took no damage, which requires winning all 5 combat rounds when the fighter has at least 51 hit points at the start. That has about a 6% chance of that happening for the usual no damage no promotions example. When it does happen, the bomber gets the number of XP specified by the EXPERIENCE_FROM_WITHDRAWL setting, which is 1 for BtS. If both units survive but the bomber takes damage, then the fighters gets this experience unless the fighter took no damage (which can only happen if the fighter started out damaged badly enough that it can't destroy the bomber even when it wins all 5 rounds, but the odds of it winning all 5 when it is so badly damaged are very low - I expect this is in there for ground units that can intercept since they never take any damage when intercepting so they will always trigger this exception).
All this is why you should clear the way with fighters first. Assuming equal promotions, it's pretty much a 50-50 fight for 2 undamaged unpromoted fighters. There is no chance that both will survive since they each need 2 hits to destroy the other and there is no way for that to not happen when the round limit is set to 5 (it would have to be way down at 2 for this to be possible). So either you eliminate a defending fighter (with a 50% chance of your fighter being undamaged and a 50% chance of being half damaged) or you don't but have a 50% chance the defender is at half damage. That is a lot better than the roughly 71.3% chance that an undamaged unpromoted fighter will shoot down an undamaged unpromoted bomber (and a 100% chance that it will intercept, preventing the bomber from doing what it was trying to do). Starting by sending in cheaper unit with a better survival chance = a good plan.
Some of the odds calculations might be slightly off, but I think this is all correct. Probably.
katipunero
Prince
God-Emperor: I wish there was a way to animate the 5 rounds of aerial battle you speak of to make things more fun. And I just realized Ive never seen a bomber gain experience from battle in IV. Your post explained the mechanics and why promotions rarely happen if they do with bombers thoroughly though.
s.bernbaum
Mostly lurking
God-Emperor: Thanks for your detailed explanation. The odds that you relate (and the fact that I usually send in lots of fighters before any bombers) makes obvious the reason for my impression stated just above your explanation, since mine was based on experience rather than looking at the code.
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