Steambirds

The plane that won the World Wars... OF STEAM!

"The Battle of London - October 15th, 1940. The Axis' flying armada is en route to London. The Allies are outnumbered 1000 to 1. You cannot save the city, but you can stall the armada long enough for London's citizens to evacuate. Good luck and Godspeed, pilot."

—Steambirds: Survival opening speech

A zany, addicting flash game series and iTouch app (The original can be found here and Survival can be found here). An Alternate History version of our timeline where, in 1835, "Sir Albert Pendleton" accidentally discovered low-temperature fusion, resulting in nuclear fusion-based steam-powered jet fighter analogues stylized in decidedly World War II design fashion.

The story is vaguely told in the mission descriptions. As can be followed, the timeline moves forward in a very In Spite of a Nail fashion, with World War I occurring in a reasonably similar fashion to our own with similar dates, albeit with heavily increased emphasis on air superiority. However, the timeline begins to diverge more in World War II, which opens with the nuking of Paris by Axis Germany. Continuing in that vein, Britain is subsequently invaded by an overwhelming German air force utilizing advanced bioweapons. Despite this, by some unknown providence of fate, they are able to push the Germans back and end the war in 1956.

Despite the less-than-plausible timeline, the game is genuinely fun, utilizing a self-contained mission structure. Within the iTunes app and first flash version, each mission provides a number of planes, typically between two and four, and a (usually) substantially larger enemy force to defeat. This is achieved by directing your planes' movement (they fire automatically when an enemy enters their firing arc) and usage of special weapons. Stars are awarded for your performance, ranging from four for not taking a hit, to one for coming out with one Hit Point left.

In Steambirds: Survival, a spin-off game, you play an Unwinnable by Design reenactment of this world's version of the Battle of Britain (called in-universe the "Gassing of London"), where you're tasked with making a Last Stand in order to buy time for escaping Londoners--ranging from orphans to Parliament--by taking as many Germans down with you as possible. You earn "copper," which is used to buy more advanced aircraft until you can buy the ~~Behemoth~~ Allurbase airship.

Tropes used in Steambirds include:

Airborne Aircraft Carrier: Subverted. Airships are present, but they don't carry aircraft. They do have wide gun coverage and an absurd amount of armor, but not complements of aircraft.
Alien Space Bats: The true point of divergence for the timeline is this, with a man discovering cold fusion twenty-five years before the American Civil War (the birthplace of modern warfare) even broke out and long before the nuclear weapon was ever invented in Real Life.
Allohistorical Allusion: Combined with Shown Their Work. Charles Babbage, who in our timeline became the father of the modern computer, is noted in the game to be the inspiration for a computer made by the Axis to crack the French Resistance's communication codes.
Alternate History: in which Steampunk jet fighters rule the skies alongside floating fortresses and airships. The timeline, Applied Phlebotinum excepted, isn't too different until World War II, where it's implied that America never joined World War I and the Soviet Union never took power in Russia.
Alternate History Wank: Britain walks cleanly out of a World War II far darker and more one-sided (and not in their favor) than ours while Germany ends with a defeat-in-detail worse than the Real Life World War I. They also consistently defeat German forces substantially larger than their own, and by the end of the game the levels are without-exception two or three British planes versus some ten or fifteen German ones.
America Wins the War: Subverted. It's implied that America (and Canada) joins neither world war. In fact, it's implied that America doesn't even care that the Germans are taking over Europe.
Applied Phlebotinum: Present in copious amounts. The "low-temperature fusion" which Sir Pendleton somehow discovered in 1835 appears to power everything, as all aircraft emit steam trails and Survival mentions fusion plants in London being dismantled to deny the Germans the assets.
Arbitrary Gun Power: Guns have arbitrary stats which, in conjunction with an armor stat, tell you how much damage your plane will do to the enemy plane's health bar.
Awesome but Impractical: The "Chickadee" fighter deployed by the British. The ace pilots demanded a plane "that wouldn't hold them back." The British responded with a plane with a very wide firing arc, high speed, impressive damage, and useful special abilities. All this came with practically no armor to speak of. Most of the pilots refuse to use the plane on these grounds.
Badass Boast: One of the story memos in Survivals is this: "Death will feast on us all, but his appetite will be sated by all these German appetizers!"
Blood Knight: One of the story memos in Survival urges the player to be this: "What men would give for this chance at glory! Kill them, brave pilot. Kill them, and laugh!"
Britain Is Only London: The Germans are implied to be invading all of Britain in Survival, but we only see the Battle of London and that is understood from the text to be the most important part of the battle.
Cool Plane: Many of the aircraft in the game--a majority of which are inspired by real planes as per Word of God--qualify for this trope, but the Looper and the Axe probably take the cake.
Color Coded for Your Convenience: Mixed with Palette Swap. The British and Germans will use the same planes sometimes, the only difference being the color (in the original, the British are always red, while the Germans vary between blue, green, and black). Some planes share the same airframe model but have different names and attributes. This could all be assumed to be Gameplay and Story Segregation, however.
Curb Stomp Battle: World War II is this in the beginning in favor of Germany, but about midway through the game the British are typically beating large enemy squadrons with only a handful of their own planes.
Deflector Shields: One of the special abilities, without so much as an accompanying Hand Wave.
Easy Logistics: Subverted. Though your planes have unlimited ammo and fuel, Survival notes that various facilities are being dismantled so that the Germans can't use them. Also, one mission in the iTouch/iPad version centers around you having run out of ammo in the last mission and therefore forcing you to rely solely on missiles.
Forced Tutorial
For Want of a Nail: Possibly blended with a Subversion of Hitler's Time Travel Exemption Act. It's not unlikely, given the way the game speaks of Germany, that the Nazis never took power in Germany.
Gameplay and Story Segregation: The number of planes seen don't add up to nearly what would be necessary to fight a world war, even if it's a locally focused on in Europe. It's also mentioned that the British stole their missile tech from the Germans, but the Germans never use this missile tech. This is probably because the game would be too hard if they did.
Ghost Town: Britain's major cities are described as becoming this in Survival, and it's played for all the depressing they can get out of it.
Guns Are Useless: Inverted. Nothing but the gun can be absolutely trusted to reliably kill the enemy in a reasonable amount of time. Missiles can back fire spectacularly and swing around to kill you rather than an opponent (this is removed in Steambirds: Survival). Poison gas (which somehow jams a plane's guns and damages its airframe) can be avoided, and your other auxiliary weapon, the bomb (once again, it goes unexplained how a bomb is hitting aircraft) depends entirely on the enemy aircraft being behind you at a specific distance to be hit.
Heroic Sacrifice: The player-character in Survival is ultimately destined to make this regardless of how good the player is. Also in Survival, a team of scientists is noted to have refused to leave their lab in Britain even under threat of mass gas bombing from Germany. They stayed on grounds of still trying to find a cure to that very poisonous gas and believing that they were very close to a cure.
Honor Before Reason: Some of the mission descriptions read as this, with British pilots sent to lure the German air force out on the understanding that they aren't coming back.
In Spite of a Nail: This timeline's world wars start right around the same time as when ours began, and their World War I even ends at about the same time. Their World War II diverges a lot, however.
Just for Pun: The second special mission involving the "Chickadee" prototype aircraft is called "Dead Turkey," a play on the phrase "Turkey Shoot."
La Résistance: The French Resistance still forms in this timeline to fight Axis Germany.
Last Stand: The British air force has one of these in Survival, fighting on purely to destroy as many enemy planes as possible and distract them from evacuating ground personnel and civilians.
Lethal Joke Character: The Looper flying wing prototype actively encourages the player to use ridiculous tactics--like full 360 degree spinning on the horizontal plane--to offset the aircraft's very narrow firing angle.
Macross Missile Massacre: The Axis leadership's final base uses a subdued form of this trope, launching an unlimited supply of missiles which fill the sky and cause incredible tactical issues with attacking the otherwise-defenseless enemy aircraft.
Misguided Missile: The missiles in the game are apparently heat-tracking and will fly until they hit a target. This target does not have to be on the opposite side of the firing aircraft, however, as it seems that the world of Steambirds did not develop IFF technology yet.
Nuke'Em: Germany's opening of World War II.
Oh Crap: An appropriate response if you fire a missile and it swings around to kill you instead of hitting an enemy. Also an appropriate response for the "true" final level of the iTouch version, which involves three enemy Behemoths with an attending squadron.
One-Man Army: If a mission starts with more than one plane under player control, all of them will likely be needed for that mission. But if you only start with one, you are guaranteed that you'll slaughter with just that plane. The player-character in Survival is made of this trope, as is the pilot of the prototype Looper flying wing aircraft.
Schizo-Tech: The nations of this Earth have missiles with no Identify-Friend/Foe technology, flying wings without stealth or advanced fly-by-wire technology, and guns which can target enemy missiles mid-flight and shoot them down. They power all of this with steam.
Shout-Out: To George Orwell's Nineteen Eighty-Four. In Survival, Japan is mentioned to have "floating fortresses tied up in China." This is also an Allohistorical Allusion; Japan was embattled in China while Germany was fighting its war in Europe, having invaded the area in 1932 in Real Life.
Steampunk: Duh.
Stupid Jetpack Hitler: Although possibly lacking in the Hitler and any trace of time travel, this world's version of Axis Germany enters World War II with nuclear and chemical weapons of surprising advancement, as their nuclear firepower is apparently sufficient to vaporize Paris.
- Actually, it's almost certainly lacking in Hitler. The games never mention one way or another, but a history nut can tell because of one key fact: Hitler did not approve of and never would have approved the use of poison gas on the battlefield. The Germans ingame... are not as principled.
Suspiciously Small Army: Neither side in either world war seems to possess nearly enough planes, although this is likely a clear-cut example of Gameplay and Story Segregation.
Take That: One of the story memos in Survival takes a potshot at British Parliament and politicians in general: "Parliament has been evacuated. Our politicians are saved! Hooray?"
Taking You with Me: The British air force's attitude in Survival towards the Germans.
Theme Naming: Each plane usually has a name that is appropriate. The Looper is designed to use 360 spins as standard tactics. The Spider is highly agile and fast, designed to spin "webs" of poison gas and run the foolish enemy pilots into it. The Duster is designed to fight in mass groups and lay unavoidable paths of poison gas. So on and so forth.
Unwinnable by Design: Survival is this by definition; there is no end to the waves of German air craft attacking you.
Weaksauce Weakness: The Chickadee is made as the perfect plane, a textbook example of a Flying Brick...except for that small problem of having no armor to speak off. Needless to say, fighting in it involves avoiding the enemy firing arc at any cost.
You Shall Not Pass: The British air force's mission in the Battle of London.
Zeppelins from Another World: The world of Steambirds still uses zeppelin airships, apparently having equipped them with heavy armor and wide-arc anti-aircraft guns.