Flying Battery Zone

"Go flying on Robotnik's warship. Watch where you step - sneaky traps are everywhere!"

- Instruction manual

Flying Battery Zone is the second zone of Sonic & Knuckles (and the eighth of Sonic the Hedgehog 3 & Knuckles), taking place after Mushroom Hill Zone and before Sandopolis Zone.

Story
After damaging Dr. Robotnik's mobile in Mushroom Hill, the player will jump at the ship and grab onto an engine as it flies away (Tails will fly up after Sonic if playing as Sonic and Tails.). They then manage to climb up onto an actual foothold and the zone begins. After defeating Robotnik, the ship begins to explode and the player breaks through a door, plummeting into Sandopolis.

Description
The level, or rather the warship the level was based on, also made a brief appearance nearing the end of Act 2 of Angel Island Zone, where it attempted to bomb the player to smithreens. It also appeared green instead of metallic gray in this instance, due to the level undergoing a massive forest fire at the time that darkened the environment.

This zone takes place on Dr. Robotnik's gigantic metal blimp. The blimp is powered by rotating drills and machines that send out worm like bridges. Flame jets can act as springs if the player stands on one for long enough, the pressure sending the character upwards; sometimes they even act as hidden switches. The mini-boss, Gapsule, is a machine that looks like one of the animal capsules. It has two huge ball-and-chain arms. The player needs to stand on the switch on top of its head and wait for it to rear back and swing. Then he/she needs to get off the machine and go out on the side in order for the machine to damage itself.

Despite the zone being one of Robotnik's contraptions, there are some Warp Rings in the level, most of which are accessed by pushing certain groups of spikes. These can be identified by a vertical pipe leading down from the floor where the spikes are, which the player can fall through.

The second act basically starts out the same, but with slightly different music.

Barrier Eggman
Very similar to the boss of Wing Fortress from Sonic the Hedgehog 2. Robotnik appears behind a barrier on one side, and a barrier on the other is activated once the player enters the arena. He'll control a laser cannon that moves along the roof, that attempts to home in on the player. Every time it attempts to do so, the barriers will close in one space. There is no special technique required for this "boss", as it eventually self-destructs after a few tries. Upon this, player needs to escape part of the Flying Battery and avoid being crushed, eventually encountering the second boss.

Hang Mobile
Robotnik appears in a lanky-armed machine that has spikes covering both arms. He'll spend time swinging around, and eventually hang below the floor, inching about with the arms. If the player jumps over the width of the machine, Robotnik shoot a blast of fire from the top. The trick is to hit the glass area -the vulnerable part- when he takes time to swing up and down around the floor. After eight hits, the scientist will speed away.

Trivia

 * According to Sonic the Hedgehog 3's (standalone) Sound Test option, this was supposed to be the fifth level in the game. Sonic (or Knuckles) was supposed to see the blimp in the carnival and be shot through the cannon (or in Knuckles' case, be transported) to the blimp. At the end of the zone, Sonic was supposed to break the door of the battery blimp and use it as a snowboard in IceCap Zone (Knuckles wouldn't get this scene because he doesn't normally snowboard). However, at that point of development, a proper transition from Mushroom Hill to Sandopolis probably wasn't thought of, so the developers decided to place Flying Battery between the two. The Sound Test option in both Sonic & Knuckles and Sonic the Hedgehog 3 places Flying Battery's music after Sounds #7 and #8 (Carnival Night's BGM). There's even an unused icon of Flying Battery leftover in Sonic the Hedgehog 3 that was supposed to appear between Carnival Night and Ice Cap. Another possible explanation for Flying Battery being placed in Sonic & Knuckles was to keep the levels between Sonic the Hedgehog 3 and Sonic & Knuckles even.
 * However, the Flying Battery Zone has no teleporter, nor any remains of a room for it. It is possible that Knuckles was never to go in the blimp.
 * Interestingly enough, while Sonic was meant to break out of the Flying Battery and use a part of it as a snowboard, it was later on reused in Sonic Adventure 2, where in the intro Sonic escapes from a G.U.N. helicopter and uses the door as skateboard.
 * Doctor Robotnik appears in the boss battle for both Sonic and Knuckles, despite Knuckles' boss battles usually being against EggRobo. The sprites for the pilot character were different for this boss battle than for any of the others, facing to the screen instead of side-on. No sprites were provided for EggRobo in this new position (for unknown reasons), Robotnik appeared instead despite EggRobo being seen earlier.
 * Supposedly, this flying fortress of metal may be used to carry animal capture Capsules. The line of capsules in the background of this stage provide evidence to this theory.
 * The Flying Battery may have attacked Sonic and Tails in Angel Island Zone before the boss. While it is identified in the manual as the "Flying Battery blimp", the size of the green underside is much smaller than the orange airship seen later.
 * This is the only zone in Sonic 3 & Knuckles (excluding non-Sonic Angel Island and the standalone Mushroom Hill) where the playable character stands still when the first act loads.
 * The ship that appears in the Sonic Generations' rendition of Rooftop Run resembles Flying Battery Zone. After opening the outside of the clock tower in Spagonia, the blimp crashes into it and Classic Sonic boards it as it starts to burn. This is possibly a completely different ship, which also looks like Sky Base from 8-bit version of Sonic the Hedgehog.
 * Both a classic mix and a remix of Act 1's music is on the Nintendo 3DS version of Sonic Generations and Mario & Sonic at the London 2012 Olympic Games, respectfully.

Music
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S&amp;K Collection
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