Aviation Ruleset

Category:Rulesets
The Aviation ruleset (github, forum thread), created and maintained by soundnfury, is focused on air warfare in the 20th Century. Unlike some other rulesets which merely add new units or mechanics to a basically Civ-like game, Aviation is close to being a total conversion. The ruleset is primarily developed for Longturn.net's freeciv21 fork of 3.1, though there is also a version targeting freeciv 3.0 (though the latter lags behind in terms of features).
As befitting the focus on air battles, land and sea forces have been heavily simplified: there are only about a dozen different ground units and a similar number of sea units — and most of the latter are aviation ships of one kind or another (aircraft carriers, seaplane tenders and helicopter ships). As for air units, there are over 100, covering not only a 60-year span of technology but also a wide variety of rôles.
Bombers, dive bombers, torpedo bombers and strike aircraft attack ground (or in some cases sea) units. Ground units can make airborne assaults either by parachute or by glider. Gliders are towed by bombers, and expended once dropped; paratroops jump from transport aircraft. Sea units can transport either carrier-capable aeroplanes, seaplanes or ground units. Airliners create trade routes between cities. Blimps and flying-boats patrol the seas, hunting submarines. Reconnaissance planes watch the enemy to find out what he's up to...
... and Fighters try to shoot down everything else!
== Key Concepts ==
Mountains are impassable to all ground units!
=== Hit Points and FirePower ===
In standard freeciv rulesets there are generally two kinds of units: pre-gunpowder, with 10 HP (and 1 FP), and post-gunpowder with 20 (and sometimes 2 FP). Thus, most fights will take 10 or more hits to kill a unit, enough that randomness will mostly be smoothed out. Aviation is not like this. There are aircraft with almost every number of hitpoints from 6 to 16, plus a few outside of this range (from the four-hitpoint ZS Zeppelin Scout to the 36-hitpoint BC Supersonic Bomber), and firepower goes up as high as 5. Most air units will take somewhere between four and eight hits from the types they're likely to be fighting, so even a small number of unlucky rolls can change the course of a fight.
Also, note that in many cases one unit's firepower won't divide evenly into the other's hitpoints, which causes all kinds of interesting effects — how strong a unit is depends to some extent on what it's fighting against. For example, having 10 HP instead of 9 is a big deal if you're fighting someone with 3 FP — they need a whole extra hit, so it's as though you had 12 HP — but makes no difference at all against an opponent with 2 FP (since either way they need the same five hits to bring you down).
=== Combat Rounds ===
Air combat is unlike the stand-up slugfest that usually constitutes fights in freeciv. Most importantly, it is not (necessarily) a battle to the death. Thematically, this is because once a bomber has dropped its bombs, it is empty; it can't just keep dropping bombs until it or the target is destroyed, it has to return home and re-arm. Similarly, if a squadron of fighters, having intercepted a bomber formation, find that they are losing the battle, they can use their superior speed to disengage, rather than fighting on until the last of them is shot down.
In Aviation this is achieved by the use of the Combat_Rounds feature which was added in 3.0: the battle will last for at most a number of rounds determined by the attacking unit type. In the case of bombers (for which attacking ends their turn), this limits how much damage they can deal, but also how much they can take from the defending unit — even the weakest of bombers will usually live to fight another day, as long as it doesn't get attacked by a fighter before it can get home.
A fighter's (or attacker's) Combat_Rounds have a slightly different effect: since the unit can keep on attacking as long as it has enough movement points, it will usually be limited more by hitpoints than by move. Instead, the CR determines the intervals at which the player can decide whether to disengage or keep fighting. However, there's another factor that comes into play when attacking a stack of units: after the first set of Combat_Rounds, when you re-engage you may be fighting a different unit, one which perhaps still has full hitpoints. Thus, a larger CR increases your chances to get kills without having to wear down the entire stack quite so far.
=== Bombardment ===
Bombarding units (Artillery and Assault Gun, as well as the Line-of-Battle Ship and Dreadnought against cities or fortresses) can't always reduce targets to 1 hitpoint like in other rulesets. Instead there is a bombardment limit below which they cannot be reduced, determined as a percentage of their full hitpoints and rounded up. This limit is:
* 15% for fortified units;
* 20% for units in a city;
* 30% for ground units in a Fortress;
* 50% for ground units in a city with the Concrete Bunker improvement.
Spotting gives a way around this, but only in the field (not in cities), and loses the advantages of bombardment (no return fire, damage all units on the tile).
=== Targets/Unreachable ===
Every unit class — ground, sea and air — is considered unreachable-by-default in Aviation. With a few exceptions like units in cities (which all count as ground for this purpose) or bases, units can only be attacked by those which target them. Broadly speaking, bombers and attackers can target ground units, torpedo-bombers and some conventional bombers can target ships, and only fighters can target other aircraft. There are a few units that cross these categories, notably strike fighters and late-period attackers which combine the ground-attack and anti-air rôles, but in general each aircraft is built for a specific purpose and can't initiate combats outside of that category.
By default, the unreachableprotects server setting is disabled, because otherwise a stack of mixed unit types would be almost untouchable.
=== Speed and Fuel ===
As with the aircraft in the classic ruleset, air units have a limited supply of fuel, and must land on a city, base or carrier before the fuel runs out or else the unit will be lost. Generally aircraft can be divided into "fast" units which have 1 fuel and can attack multiple times per turn, and "slow" units which have 2 or more fuel but which end their turn on attacking. There are a few exceptions however: blimps, helicopters and escort-fighters can all multiattack, but have multiple fuel, allowing them to loiter on-task for various reasons.
Aircraft are much faster across the map than anything else; by the jet age, they can fight battles as much as 15 tiles away from their base. Since some aircraft can also deliver ground troops to capture cities, the 'front line' can be very deep — a poorly-defended city in the middle of your empire might suddenly fall to a long-range airborne assault.
The second veteran level (ace) gives aircraft an extra move point, which thus extends their range; this is distinctly useful in the early era (for some early heavy bombers it could be as much as a 25% gain), but by the jet age it's a mere drop in the bucket.
=== Trade and Blockades ===
An important driver of the game's economy is the Merchant Ship, which travels to foreign cities and enters the marketplace there to be converted into gold and bulbs. (You can also use it to trade between two of your own cities, but then you will only get gold, not bulbs.) Since this will (at least over decently long routes) yield rather more than building Export (i.e. Coinage, turning shields directly into gold at a 1:1 ratio), a trading civilisation can pull ahead in science and often not need gold tax at all.
However, Merchant Ships are quite vulnerable; with only 6 hitpoints, they can be sunk by a wide variety of units (submarines, torpedo-bombers, flying-boats, and some conventional bombers), meaning that a hostile power may be able to strangle your maritime trade routes. (Later in the tech tree there is the Catapult Armed Merchantman, which has triple defence against air attack, but it's still pretty weak.) Much of the importance of naval aviation in the game is to either protect your own merchants (Sea Control) or interdict the enemy's (Sea Denial), either directly or via submarines (which are themselves somewhat vulnerable to air attack).
Merchant Ships can also be captured (taken as Prizes) by some units (surfaced submarines, helicopters, and battleships), allowing you to steal someone else's trade-goods for your own. But only a lone ship can be captured; convoying prevents this. Moreover, taking a prize ends a sub or helicopter's turn, making them vulnerable to retaliation.
Land-locked nations can still trade by means of the Merchant Truck, but it moves very slowly, delaying the pay-off and costing more turns of upkeep in the meantime.
One-time trade revenue depends only on the distance between the source and destination cities, not their trade output. (It can, however, be boosted 12½% by the smallwonder Lloyd's of London.)
Persistent trade routes between cities are also important; instead of the classic ruleset's Caravan and Freight, these are created with airliner units. Thanks to fuel, these have a limited range, so unless there are convenient allied cities or empty airfields to refuel at, you won't be able to create truly globe-girdling trade routes. Still, the routes you can create will earn plenty of trade for both ends. Beware, though, that airliners are completely defenceless, should some hostile power send in a fighter to catch them en route. Also, the number of trade routes a city can have depends on various buildings (and a wonder, ICAO); without any of them, the limit is 1.
=== Airborne Assault ===
Moving ground units around is slow. Most only have 1 move, and even the Landing Craft which can transport them across the sea only has 2 move. Roads don't speed them up at all, and even railways take half a movement point to traverse. If you want to fight a blitzkrieg, you need to deliver ground forces from the air. Without a friendly city or airfield to land at and unload, this can be difficult; there are three ways to do it: gliders, paras and helis.
Note that only Assault-class units can be transported in this way; the Troops and Artillery units are too heavy to travel by air (or by landing-craft), though they can still cross the seas in the Troop Ship if there is a friendly city to unload at. 
==== Gliders ====
A glider is an air unit with zero move, which can carry a number of assault units, and can itself be 'carried' by certain aircraft (tugs), namely medium and heavy bombers from the 1920s through to the mid-’40s. The bomber tows the glider to the Drop Zone, then unloads it (it must be flat ground, i.e. not forest or jungle); next, the assault units unload from the glider and fight their ground battles. The glider is thus single-use (you may as well disband it afterwards), but that's okay because it's pretty cheap.
In the ’40s, the Heavy Glider adds the ability to carry the Light Tank unit.
==== Parachutes ====
The Paratroops unit works a bit differently to classic freeciv. Instead of having a special Paradrop action, its distinguishing feature is that it can unload from a transport aircraft in flight. As well as dedicated military transports, some heavy bombers and even flying-boats can carry a small number of units. After unloading, the paras are immediately ready to fight. Though they avoid the complicated faff of discarding a glider, they aren't quite as good as gliderborne troops at holding on to their gains, and you can't paradrop artillery (the airlanding Assault Gun is a low-powered bombardment unit).
==== Helicopters ====
Once you develop gas-turbine-powered helicopters, you can use them to deliver units anywhere. Because a heli can land in a field without a prepared airstrip, assault units can unload from it directly, without all that tedious mucking about with gliders. The main downside is the helicopter's short range.
The ’60s Twin Rotor can carry light tanks.
=== Heavies and Jets ===
Some large four-engined aircraft have the heavy flag, which means they can only repair in a city with the Concrete Runway improvement.
Once the gas-turbine jet engine arrives, many of the new aircraft are far more advanced than their predecessors. Most prop planes can't be upgraded to jets (some have a parallel 'superprop' and/or 'turboprop' line), and most jets can only be built (or repaired) in a city with the Air Base improvement. (The exceptions include "light fighters", VTOL aircraft, and the Jet Flying Boat.)
== Economy ==
At present, the ruleset's economy is rather underdeveloped. There are buildings to boost sci/tax/lux production (Aeronautical Library, Technical College, Wind Tunnel, Commercial Airstrip, Int'l Airport, Balloon Rides, Airship Company, Air Tours, Travel Agent) as well as content-citizen buildings (Flying Club, Air Races) and the police-station-like War Memorial to mitigate military unhappiness. To limit corruption, the FAA Branch acts like a classic Courthouse. This is a much less multiplicative economy than the classic ruleset (with its three levels of Library/University/Research and Marketplace/Bank/Stocks); in Aviation the way to get rich is through foreign trade. This means that you need to (a) have at least some friendly neighbours, and (b) protect your merchant marine from any unfriendly neighbours.
Buildings like Crop Dusting (analogous to classic Supermarket), Waterbombers, Coast Guard and Marshalling Yard increase tile output, while Lumber Yard, Power Plant, Engine Factory and Aircraft Factory boost shields (à la Factory and Mfg Plant) and in some cases give additional Build Slots. Tramways and Electrification combat pollution, broadly resembling the classic Mass Transit and Recycling Centre. Recruiting Office reduces unit upkeep (but only if your government pays in shields, not gold); University Air Squadron does the same but only for Democracies.
For supporting your military, the Barracks does what you'd expect, and Shipyard is like a Port Facility. For air units there are separate buildings for veterancy (Flying School) and fast HP recovery (Repair Sheds for landplanes, Aircraft Slipways for seaplanes). Flak Battery and SAM Battery give cities defensive bonuses against aircraft; Barrage Balloons protect specifically against dive-bombers; Sector Control gives a small bonus to scrambling fighters, while Concrete Bunker partially protects units in the city from artillery bombardment. Concrete Runway is required to repair heavy bombers, while an Air Base is needed to repair or build most jet aircraft. A Radar Station increases a city's vision range.
Wonders are a bit of a grab-bag; there are some economic ones (Lloyd's of London, Kitty Hawk Monument, Aeronautical Institute, de Havilland, National Airline, Hub Airport, Supersonic Wind Tunnel), happiness (Statue of the Generals, Display Team, Human In Orbit) a leonardo (SBAC Airshow, halves upgrade prices), tech stealing (Jane's All The World's Aircraft, KGB Headquarters), and a couple of darwins (Schneider Trophy, Sound Barrier). Staff colleges give units increased chances of gaining veteran levels (War College for ground-troops, Naval College for ships, seaplanes and carrier aviation, RAF College Cranwell for landplanes). The Yasukuni Shrine allows a Fascist nation to build Kamikazes; Manhattan Project allows everyone to build nuclear bombs. Chain Home gives radar-station vision to every city on the continent, while Shipping Forecast increases the move rate of sea units. ICAO reveals all cities, and gives every city (for all players) an extra trade route; Spy Satellites reveals the whole map (but not units).
=== Government ===
The available governments are rather different to classic freeciv. In particular, none of them have any tech requirements — by 1900 they've all been invented already.
==== Constitutional Monarchy ====
You start the game as a Monarchy. This government has moderate corruption, but pays upkeep in gold (rather than shields), and can use up to 2 units of martial law to keep citizens content. On the other hand, unhappiness due to empire size is something of a problem (base 10, step 9), and it also experiences unhappiness from aggressively deployed military units.
==== Democracy ====
In Democracy, corruption is unaffected by distance from the capital (though the baseline is a little higher), and each tile gets +1 trade; celebrating cities get another +1 on top of this. It suffers unhappiness from aggressively deployed military units, and has a Senate which may prevent you from declaring war. For farming your economy there's nothing to beat it, as long as you can keep everyone happy.
==== Communism ====
Corruption is lower than Monarchy but still varies with distance. There is also waste of shields, and Communists are bad at science (40% penalty) and produce more pollution (+50% to shield-based pollution). However, it gets two extra content citizens per city, and up to three units may impose martial law. Thus, it can be useful for militaristic rampages.
Communists may build the KGB Headquarters smallwonder, which steals any tech known by at least two other players. (If they have Jane's as well, they get any tech known by a single other player.) This goes some way towards mitigating their own slow research.
==== Fascism ====
The Fascists also like their militaristic rampages; they too get two extra content citizens per city and three units of martial law. They can build the Kamikaze unit, spending population to destroy enemy ships. They also get certain units upkeep-free (dive-bombers, Early Heavy Fighter, Kamikaze, Artillery Rocket, Swept-Wing Fighter, Paratroops, Assault Troops and the Assault Gun); for other units they pay upkeep in gold, but at double the rate. Corruption is severe. Fascism has the lowest unhappiness due to empire size (base 15, step 16). Can you conquer the world before your economy collapses?
== Military ==
=== Ground units ===
There are not many of these. There is one main city defender, Troops, which lasts un-upgraded throughout the entire tech tree; it's unable to travel on transports other than the Troop Ship. Nor is the Artillery, a reasonably powerful bombarder. If you have a hostile land border you might end up fighting trench warfare with lines of troops and arty (possibly with fortresses standing in for the trenches) but it'll be somewhere between 'stalemate' and 'meatgrinder'. If someone leaves a city undefended, you might be able to ship in some Marines to snatch it, but they're very weak in combat.
The main attacking units are the Assault Troops and Paratroops, both of which are designed to be delivered from the air in surprise attacks. There's also the Assault Gun, an airliftable bombarder that's quite handy for reducing big stacks (but isn't quite as strong as Artillery), and the Light Tank which is a stronger defender than Assault Troops but can only be carried by heavy gliders and strategic transport aircraft.
The Radar Van can drive out to an open tile and then convert into the Radar Tower, giving vision similar to (but shorter than) a Radar Station in a city, but both are vulnerable.
And of course there are the non-military Settlers and Seabees (workers), which have a very slight defensive ability (and which, incidentally, always cost 1 gold upkeep (plus 1 food for Settlers), regardless of government).
=== Ships ===
The purpose of sea-power is found in the Merchant Ship (for trade) and the Landing Craft (a troop transport, good for amphibious invasions or for carrying settlers to colonise unoccupied islands). There's also the Catapult-Armed Merchantman, a slightly more expensive merchie with quintuple defence against aircraft, and the Troop Ship which can carry heavy infantry and artillery but needs a friendly city to unload.
The Submersible is a tool of sea denial; it can surface (convert unit) for extra speed, then submerge for stealth and greater attack strength; however, its limited supply of air and battery-power must be regularly replenished by coming to the surface. The later U-Boat extends the underwater endurance, while the nuclear-powered SSN doesn't need to surface at all (and is as fast underwater as U-Boats are on the surface). Surfaced submarines can also capture lone merchant ships (take prize).
Sea control can rest on gun-toting warships like the Line-of-Battle Ship and Dreadnought, which can also bombard cities or fortresses up to two tiles away, but their rôle is gradually usurped by various aviation ships. The Seaplane Tender can refuel floatplanes, flying-boats and blimps, useful early on but then outclassed by carrier-borne aircraft. Those can fly from the Light Aircraft Carrier, Aircraft Carrier, Escort Carrier and Nuclear Aircraft Carrier; of these the CVL, CV and CVN form a progression of increasing capacity, speed and defence, while the CVE is a converted merchant ship which can cheaply supply a little air cover to a convoy. (After the invention of the CVL, old Line-of-Battle Ships can be converted to it, though this takes 3 turns.) The Heli Assault Carrier transports helicopters, which may in turn be carrying assault troops for an invasion, or just tasked with ASW.
All sea units gain a point of speed when the player builds the Shipping Forecast smallwonder.
=== Aircraft ===
There are so many of these that rather than listing them all here, I'll speak in generalities, and refer the reader to either the in-game help or the recognition chart for specifics.
On attaining the second veteran level (Ace), air units gain an extra point of speed.
==== Bombers ====
There are four main kinds of bombers: light, medium, heavy and dive. The heavy bombers deal a lot of damage, but are vulnerable to fighters; conversely, light bombers are robust (relative to their price) but only scratch at targets. Medium bombers are a balance between offence and defence. Dive bombers are an ultra-attacking option: they generally combine the offence of a medium and the cost of a light with defence weaker even than a heavy. Dive bombers and some light bombers are carrier-capable. While all bombers can attack ground units, some can also strike at ships. Most mediums can tow gliders, and some heavies can do the same or carry ground units directly (such as paratroops).
Later heavy bombers can convert into 'modified' versions which drop special bombs such as hardened penetrators or nukes.
One very early bomber is the Zeppelin Bomber. It deals only a little damage and is highly vulnerable to fighters, but if the enemy hasn't invented fighters yet it just might have a use. (It's also by far the earliest air transport available, though it's not that much faster than ships or even walking.)
Once the technology Incendiary Bomb has been researched, some bombers (medium, heavy, and zeppelin) can firebomb cities, causing the city to have 50% less shield production on the following turn.
Maritime patrol aircraft derived from heavy bombers are optimised for the anti-submarine warfare rôle.
==== Torpers ====
Built purely for attacking sea units, torpedo-bombers are hard-hitting but flimsy (they particularly suffer when attacking fighters on a carrier). The early floatplanes are soon overtaken by carrier-borne equivalents.
They can't bomb ships in port, only on the open seas. (This is thanks to a ruleset workaround for a game engine limitation.)
==== Flying-boats ====
These are mostly light or medium bombers, generally able to attack land or sea targets, but more expensive and less powerful than landplane equivalents. On the other hand, they are longer-ranged, especially if supported by tenders. Some of them can carry ground units.
The Jet Flying Boat is a cross between an attacker and a fighter; it's just all-round weird.
==== Blimps ====
Cheap and able to loiter (4 fuel), these can attack sea units, but not very powerfully — their primary purpose is hunting submarines.
==== Attackers ====
Ground-attack aircraft have multiattack, meaning they don't have to wait around for a turn and give enemy fighters a chance at them. However, they're typically short-ranged and not as powerful as bombers, making their use in battle more tactical than strategic. Near the end of the tech tree, some attackers gain the ability to target sea and/or air units; and there are also carrier-capable attackers.
==== Reconnaissance ====
Various aircraft from around the tech tree have the ability to Investigate City. Some are purpose-built for recon (including the low-tech Zeppelin Scout, which is long-ranged but slow), while others add it to other rôles (mostly light and later medium bombers). The Early Helicopter and Helicopter have the unusual ability to see submarines from more than one tile away. The extremely early Pioneer has the distinction of always being built as veteran, although since its combat stats are zero this is only of use once it upgrades to something else.
Some light bombers and floatplanes can Spot for artillery or naval gunfire. Spotting a target on land (outside of a city) allows artillery units to attack it rather than bombarding, potentially allowing their best-in-class attack strength to kill units rather than merely damaging them; meanwhile, battleships and dreadnoughts get a 25% attack bonus against spotted ships at sea. Spotting ends the aircraft's turn unless the player has discovered Radio.
==== Transports ====
For either shuttling units quickly between your cities, or delivering paratroops to their objectives. These aircraft have no combat capability, so beware of fighters. However, they can carry a lot more units than will fit in, say, a heavy bomber.
There's also the Helicopter, which can unload units in the field.
==== Tankers ====
In-flight refuelling (implemented by carrying aircraft 'inside' the tanker) can extend an aircraft's range, or allow it to remain continuously airborne (by cycling from one tanker to another) to ensure second-strike capability (as long as the unit's homecity doesn't fall).
==== Fighters ====
Generally built for one purpose only: shooting down enemy aircraft. (There are occasional exceptions, like the Naval Strike Fighter, which combine fighter and attacker rôles, but these are generally less effective in air-to-air combat than dedicated fighters.) Besides the main progression of single-seat fighters (from WWI scouts through WWII monoplanes to postwar jets) there are a few side-options which have some (usually transient) advantages. Triplanes have a brief combat advantage but are a technological dead end, while two-seat fighters (later developing into turret fighters) are an idea that comes and goes, occasionally being stronger than single-seaters. Heavy fighters have 2 fuel, meaning they can stick around to escort bombers, but being less nimble, they are at a disadvantage in combat. The jet age brings the 'light fighter' concept, cheap to build (no Air Base required) but weaker than cutting-edge designs.
Seaplanes and flattops also get their own fighter families, generally weaker than the land-based equivalents (but then, the things they're likely to be fighting — other seaplanes, torpedo-bombers and dive-bombers — aren't that strong either).
==== Bombs ====
The Penetrator Bomb can be used for a Precision Strike to destroy a selected city improvement; it's also effective against battleships and dreadnoughts (the "Tirpitz rule").
You can only have one Atomic Bomb, but its nuclear blast destroys all the units in a 3×3 square (including, unfortunately, the bomber that drops it). The Thermonuclear Bomb removes the uniqueness limit, allowing you to build up a stockpile; the Stand-Off Bomb (carried only by advanced jet bombers) can fly up to four tiles before exploding, allowing the launch aircraft to escape the nuclear blast.
==== Missiles ====
The Artillery Rocket is straightforward enough — effectively just a cheap bomber that's destroyed after attacking. But the Kamikaze, designed to attack ships, has a bunch of requirements: to build it you need to have a Fascist government, and have built the smallwonder Yasukuni Shrine. While it's cheap in shields, it also costs 1 population to build, so blowing up too many of these can gouge deep into your economy.
The Surface-to-Air Missile, with its two-tile range, can bring down enemy aircraft, but it can't scramble (it has zero defence).
==== Civilian aircraft ====
Make embassies with the Ambassador. Establish trade routes with airliners — these need a Commercial Airstrip in the city that builds them, apart from the lighter-than-air Zeppelin Liner which instead needs a Mooring Mast. (Either of those buildings will unlock a city's second trade route slot.)