Rapidfire has been questioned since the beginning of the Ogame world, so I'm going to try to stop that.
Rapidfire means what it says on the tin, that a ship will fire more than once in a round, but when and why?
The answer... Example: If ship A has Rapidfire of 5 against ship B, and ship A manages to hit and destroy ship B, ship A has an 80% chance that it will fire again. If, on the second shot, ship A hits and destroys another ship of the same type as ship B again, it has 80% chance of firing again, and so on...
The percentage chance of ship A firing again can be worked out by finding out what rapidfire it has against ship B (in this case 5), dividing 100 by it (100/5=20), and then taking the result away from 100 (100-20=80% chance). The number of Rapidfire that ship A has against ship B is the average of how many ship B's ship A destroys per round.
So, again, Ship A has Rapidfire of 5 against Ship B. Ship A hits and destroys a Ship B. Ship A gets an 80% chance of firing again, so 4 out of 5 times, Ship A will fire again. So if the computer calculates a number between 0 and 100, if the number is below 80, then Ship A will fire again, if its above, it must wait until the next round to fire again.
But remember, a ship could have 99% chance to fire again but not even once more, so don't assume you'll actually destroy that many.
So without further ado, the Rapidfire of all ships and defence and their % chance of firing again.
Small Cargo Ship
Rapidfire against Espionage Probe: 5 (80% Chance)
Rapidfire against Solar Satellite: 5 (80% Chance)
Rapidfire of Heavy Fighter against this Ship Type: 3 (66.6% Chance)
Rapidfire of Battlecruiser against this Ship Type: 3 (66.6% Chance)
Rapidfire of Death Star against this Ship Type: 250 (99.6% Chance)
Large Cargo Ship
Rapidfire against Espionage Probe: 5 (80% Chance)
Rapidfire against Solar Satellite: 5 (80% Chance)
Rapidfire of Battlecruiser against this Ship Type: 3 (66.6% Chance)
Rapidfire of Death Star against this Ship Type: 250 (99.6% Chance)
Light Fighter
Rapidfire against Espionage Probe: 5 (80% Chance)
Rapidfire against Solar Satellite: 5 (80% Chance)
Rapidfire of Cruiser against this Ship Type: 6 (83.3% Chance)
Rapidfire of Death Star against this Ship Type: 200 (99.5% Chance)
Heavy Fighter
Rapidfire against Espionage Probe: 5 (80% Chance)
Rapidfire against Solar Satellite: 5 (80% Chance)
Rapidfire against Small Cargo: 3 (66.6% Chance)
Rapidfire of Battlecruiser against this Ship Type: 4 (75% Chance)
Rapidfire of Death Star against this Ship Type: 100 (99% Chance)
Cruiser
Rapidfire against Espionage Probe: 5 (80% Chance)
Rapidfire against Solar Satellite: 5 (80% Chance)
Rapidfire against Light Fighter: 6 (83.3% Chance)
Rapidfire against Missile Launcher: 10 (90% Chance)
Rapidfire of Battlecruiser against this Ship Type: 4 (75% Chance)
Rapidfire of Death Star against this Ship Type: 33 (97% Chance)
Battle Ship
Rapidfire against Espionage Probe: 5 (80% Chance)
Rapidfire against Solar Satellite: 5 (80% Chance)
Rapidfire of Battlecruiser against this Ship Type: 7 (85.7% Chance)
Rapidfire of Death Star against this Ship Type: 30 (96.6% Chance)
Colony Ship
Rapidfire against Espionage Probe: 5 (80% Chance)
Rapidfire against Solar Satellite: 5 (80% Chance)
Rapidfire of Death Star against this Ship Type: 250 (99.6% Chance)
Recycler
Rapidfire against Espionage Probe: 5 (80% Chance)
Rapidfire against Solar Satellite: 5 (80% Chance)
Rapidfire of Death Star against this Ship Type: 250 (99.6% Chance)
Espionage Probe
Rapidfire of Small Cargo Ship against this Ship Type: 5 (80% Chance)
Rapidfire of Large Cargo Ship against this Ship Type: 5 (80% Chance)
Rapidfire of Light Fighter against this Ship Type: 5 (80% Chance)
Rapidfire of Heavy Fighter against this Ship Type: 5 (80% Chance)
Rapidfire of Cruiser against this Ship Type: 5 (80% Chance)
Rapidfire of Battle Ship against this Ship Type: 5 (80% Chance)
Rapidfire of Battlecruiser against this Ship Type: 5 (80% Chance)
Rapidfire of Colony Ship against this Ship Type: 5 (80% Chance)
Rapidfire of Recycler against this Ship Type: 5 (80% Chance)
Rapidfire of Bomber against this Ship Type: 5 (80% Chance)
Rapidfire of Destroyer against this Ship Type: 5 (80% Chance)
Rapidfire of Death Star against this Ship Type: 1250 (99.92% Chance)
Bomber
Rapidfire against Espionage Probes: 5 (80% Chance)
Rapidfire against Solar Satellite: 5 (80% Chance)
Rapidfire against Missile Launcher: 20 (95% Chance)
Rapidfire against Small Laser: 20 (95% Chance)
Rapidfire against Heavy Laser: 10 (90% Chance)
Rapidfire against Ion Cannon: 10 (90% Chance)
Rapidfire of Death Star against this Ship Type: 25 (96% Chance)
Solar Satellite
Rapidfire of Small Cargo Ship against this Ship Type: 5 (80% Chance)
Rapidfire of Large Cargo Ship against this Ship Type: 5 (80% Chance)
Rapidfire of Light Fighter against this Ship Type: 5 (80% Chance)
Rapidfire of Heavy Fighter against this Ship Type: 5 (80% Chance)
Rapidfire of Cruiser against this Ship Type: 5 (80% Chance)
Rapidfire of Battle Ship against this Ship Type: 5 (80% Chance)
Rapidfire of Battlecruiser against this Ship Type: 5 (80% Chance)
Rapidfire of Colony Ship against this Ship Type: 5 (80% Chance)
Rapidfire of Recycler against this Ship Type: 5 (80% Chance)
Rapidfire of Bomber against this Ship Type: 5 (80% Chance)
Rapidfire of Destroyer against this Ship Type: 5 (80% Chance)
Rapidfire of Death Star against this Ship Type: 1250 (99.92% Chance)
Destroyer
Rapidfire against Espionage Probes: 5 (80% Chance)
Rapidfire against Solar Satellite: 5 (80% Chance)
Rapidfire against Small Laser: 10 (90% Chance)
Rapidfire against Battlecruiser: 2(50% Chance)
Rapidfire of Death Star against this Ship Type: 5 (80% Chance)
Battlecruiser
Rapidfire against Espionage Probe: 5(80% Chance)
Rapidfire against Solar Satellite: 5(80% Chance)
Rapidfire against Small Cargo: 3(66.6% Chance)
Rapidfire against Heavy Fighter: 4(75% Chance)
Rapidfire against Large Cargo: 3(66.6% Chance)
Rapidfire against Cruiser: 4(75% Chance)
Rapidfire against Battleship: 7(85.7% Chance)
Rapidfire of Destroyer against this Ship Type: 2(50% Chance)
Rapidfire of Deathstar against this Ship Type: 15(93.3% Chance)
Death Star
Rapidfire against Espionage Probe: 1250 (99.92% Chance)
Rapidfire against Solar Satellite: 1250 (99.92% Chance)
Rapidfire against Small Cargo Ship: 250 (99.6% Chance)
Rapidfire against Large Cargo Ship: 250 (99.6% Chance)
Rapidfire against Light Fighter: 200 (99.5% Chance)
Rapidfire against Heavy Fighter: 100 (99% Chance)
Rapidfire against Cruiser: 33 (97% Chance)
Rapidfire against Battle Ship: 30 (96.6% Chance)
Rapidfire against Battlecruiser: 15 (93.3% Chance)
Rapidfire against Colony Ship: 250 (99.6% Chance)
Rapidfire against Recycler: 250 (99.6% Chance)
Rapidfire against Bomber: 25 (96% Chance)
Rapidfire against Destroyer: 5 (80% Chance)
Rapidfire against Missile Launcher: 200 (99.5% Chance)
Rapidfire against Small Laser: 200 (99.5% Chance)
Rapidfire against Heavy Laser: 100 (99% Chance)
Rapidfire against Gauss Cannon: 50 (98% Chance)
Rapidfire against Ion Cannon: 100 (99% Chance)
Missile Launcher
Rapidfire of Cruiser against this Ship Type: 10 (90% Chance)
Rapidfire of Bomber against this Ship Type: 20 (95% Chance)
Rapidfire of Death Star against this Ship Type: 200 (99.5% Chance)
Small Laser
Rapidfire of Bomber against this Ship Type: 20 (95% Chance)
Rapidfire of Destroyer against this Ship Type: 10 (99% Chance)
Rapidfire of Death Star against this Ship Type: 200 (99.95% Chance)
Heavy Laser
Rapidfire of Bomber against this Ship Type: 10 (90% Chance)
Rapidfire of Death Star against this Ship Type: 100 (99% Chance)
Gauss Cannon
Rapidfire of Death Star against this Ship Type: 50 (98% Chance)
Ion Cannon
Rapidfire of Bomber against this Ship Type: 10 (90% Chance)
Rapidfire of Death Star against this Ship Type: 100 (99% Chance)