Now you've got me curious, starlifter. What DOES an airbase do foodwise? I know it doesn't duplicate farmland and irrigation precisely because it will enhance food output from Spice and Fruit, for example, on terrain that cannot be farmed. Plus, there's the +1 food to mountains thing that no other terrain improvement can cause. Yet it doesn't stack with farmland or irrigation.
So what does it do?
LOL, I knew someone might ask that

. I now have license for a 10,000 character post, hehe....
A. An Airfield does
exactly the following (with respect to food), in the following order... no more, no less:
1. Acts as IRRIGATION on any land terrain in the game.
2. Acts as FARMLAND on any land terrain in the game.
(It really is that simple)
B. The
confusion is primarily because of 2 things:
1. People may not
really understand IRRIGATION and FARMLAND.
2. Engineers/Settlers are
seemingly not "allowed" to IRRIGATE and FARM all terrain in the game.
So the real question is not about airfields, but about basic IRRIGATION and FARMLAND!
Lets take this by example. Start Civ II, in a game that has engineers in it. Move an engineer to an unimproved chunk of Plains or Grassland. Click the ORDERS pull down menu. Look at the options. An option will be Irrigation. This is explicitly programmed by the game designers. now irrigate the land and go for 3 turns. The land will now be irrigated. Go back to the ORDERS menu. Now note the "I" option. It has changed to "Improve farmland". With it, you can make farmland.
Repeat the above example on an unimproved mountain. Note that the "Build Irrigation" option is
greyed out. The game designers did not want you IRRIGATING mountains.
Repeat the above example on an unimproved hill. Note that the "Build Irrigation" option is
not greyed out. The game designers
did want you IRRIGATING hills (if you chose to do so).

You can also make Farmland in hills. But hills have a special restriction (which arises from an unrelated issue that I won't discuss at this time)... if a MINE exists, the effect of mining is LOST as long as the irrigation exists. You cannot have both irrigation and mines at the same time.
Repeat the above example on an unimproved jungle-fruit. Note that the "Build Irrigation" option
is changed. You CANNOT irrigate! It is simply not an option. But you can "Change to Grassland". The game designers did not want you IRRIGATING jungle-fruit.

HOWEVER... you can transform to plains, or change to forest and change to plains ('irrigate' the forest), or Change to Grassland, make a forest, and change to plains. So guess what? You will have Wheat... which can then be irrigated and farmed.
Now from these examples, you can likely deduce the exact nature of irrigation and farmland, if you have it in a city radius and used a Supermarket.
But for completeness, this is it:
Irrigation (not the ORDERS --> "i" key, but actual IRRIGATION) simply adds one food to terrain types that the
programers and Sid Meier chose to allow. Farmland applies the 50%, rounded down bonus. If a terrain produces one food, 50% of 1 is .5, which is ZERO. Hence, farmland in a desert does not increase available food even with a supermarket. Ditto for Jungle-Gems. Ditto for forests.
All this is "programmed" type by type in the RULES.TXT file. Here is a summary of the standard Civ II terrain production:
Desert, 1,2, 0,1,0, yes, 1, 5, 5, yes, 1, 5, 3, Pln, ; Drt
Plains, 1,2, 1,1,0, yes, 1, 5, 1, For, 0,15, 0, Grs, ; Pln
Grassland, 1,2, 2,1,0, yes, 1, 5, 2, For, 0,10, 0, Hil, ; Grs
Forest, 2,3, 1,2,0, Pln, 0, 5, 5, no, 0, 5, 0, Grs, ; For
Hills, 2,4, 1,0,0, yes, 1,10, 0, yes, 3,10, 1, Pln, ; Hil
Mountains, 3,6, 0,1,0, no, 1,10, 0, yes, 1,10, 6, Hil, ; Mou
Tundra, 1,2, 1,0,0, yes, 1,10, 1, no, 0, 0, 0, Drt, ; Tun
Glacier, 2,2, 0,0,0, no, 0, 0, 0, yes, 1,15, 3, Tun, ; Gla
Swamp, 2,3, 1,0,0, Grs, 0,15, 6, For, 0,15, 0, Pln, ; Swa
Jungle, 2,3, 1,0,0, Grs, 0,15, 6, For, 0,15, 0, Pln, ; Jun
Ocean, 1,2, 1,0,2, no, 0, 0, 0, no, 0, 0, 0, no, ; Oce
In Mountains, you see a grouping "
no, 1,10,0" which means respectively, "
Irrigate, bonus, #turns, ai-irrigate". This means the ORDERS --> "i" key will be greyed out. It means the irrigation will cause 1 (That's RIGHT.... ONE!) food (Assuming one COULD irrigate!). It means it
would take 10 turns to irrigate (Assuming one COULD irrigate!). It means the AI will never, ever try to irrigate a mountain.
Now the only issue remaining is how we irrigate & farm terrain, like a mountain, that does
not have the ORDERS --> "i" option available, but for which Sid Meier decided you could indeed irrigate and farm. The answer is AIRFIELDS.
Look at
Mountains... If Sid had wanted a mountain never to be irrigated under any circumstances, he could have used the "no,0,0,0 " option like he did for ocean and GLACIER terrain!!
Instead, he alllowed a back-door (meaning not well known) way of irrigating a mountain.... a late game airfield!!!
Look at
Forests.... "Pln, 0, 5, 5," This means the forest will be changed to Plains in 5 settler turns, and the AI will not EVER try to "irrigate" (Change to Plains) a forest unless it is in Monarchy or above.
Look at
Hills... "yes, 1,10, 0," The hills can be irrigated in 10 turns and will give a 1 food bonus. The AI will not EVER try to Irrigate hills.
Farmland/Supermarkets are hard-coded. If a tile has the farmalnd or airfield flag set, a 50% bonus, rounded down, is applied. This occurs AFTER the irrigation bonus is applied. Thus, irrigating plains gives 1+1=2 food. Farmland is 2*50%=extra food (2+1=3 TOTAL food). For a mountain, 0+1=1 (possible with only an airfield). The airfield's deliberate farmland bonus is : 1*50%=0.5=0 extra food (1+0=1 TOTAL food).
Look at
Jungle-Fruit.... a 4 food base output. If you "i" the tile, it becomes grassland. So you must use the airfield (available only in late game). Then: Irrigation is 4+0=4 (you get no jungle irrigation effect.... look it up: "Grs, 0,15, 6, "). But guess what... the farmland effect applies: 4*50%=2 extra food (4+2=6 TOTAL food). Note what happens if you convert the Jungle to Plains... you get Wheat, and teh result is EXACTLY the same in the end: 6 food! So there is no special advantage, or any net gain by using airfields even on Jungle-Fruit. Exactly the intended effect occurs.
On your own, examine Glaciers... Tundra... Swamps.... Oceans... You'll see everything is specifically designed and set for the intended game balance a certain way. But the designers of Civ II chose to allow you (and scenario makers) to alter these items, if you wanted.... the RULES.TXT.
Since this is a long post, I know most people will never read nor understand it, and that's OK. But this is an easier part to see and understand than the actual game programming (decompilations). It clearly shows how Matrix or anyone else can simply alter the "programming" to OVERRIDE the choices that Sid Meier and company have made for years.... simply revise the rules.txt and require that all GOTMs are played with it. Quite trivial, LOL.
So,
Airfields are NOT a cheat, even when used for irrigation! And the "bug" part of airfields is
not in their behavior (which is knowingly and deliberately set by Sid & Co.), but in their relative construction time (two turns). IMHO, additional programming should have been done to increase construction time in difficult terrain. But it is hard coded to 2 turns. Oh well. A slight difference of opinion between me and the game's designers, LOL.
BOTTOM LINE: The Airfields behave
exactly the way Sid Meier and Brian Reynolds intended them. Indeed, they
chose for them to behave that way!
The behavior is programmed,
but can be altered in the RULES.TXT by anyone who desires to substitute their judgement for the designers of the game. (even
you can change it, Chofritz,

).
Questions?
This post is 8,454 characters long...