The series consists of six main games in the series, some of which were compiled for later releases.
This game, the start of the series, was released in 1983, predating the Nintendo Entertainment System. The game did not receive a stateside release, but was released on several Japanese home computer systems, including Sharp, NEC, and Fujitsu's home computer platforms. The game uses a top-down camera angle similar to Namco's Xevious, and like Xevious, the character's ship only has two weapons – a forward firing short-range bomb for use against ground targets, and the ship's main gun.
The story introduces the conflict between the Galactic Federation (which is later revealed to not contain Earth), and the malevolent ORN empire. The player, controlling the FIRE LEO starfighter, is assigned to destroy ORN's asteroid fortress Dyradeizer.
Thunder Force II
After the destruction of the fortress Dyradeizer in the first game in the series, the ORN Empire, while it has experienced a setback, is not yet defeated. The Empire has begun work on a massive new battleship, called the Plealos, underneath the surface of the planet Nebula. With this new massive warship at their command, the ORN Empire can set out on a new offensive against the Galactic Federation that could potentially destroy it. In response to this new threat, the Galactic Federation sends their new starfighter, the FIRE LEO-02 Exceliza to Nebula to destroy their bases upon the service, and finally the Plealos itself.
While this game continues to use the top-down camera angle that was used in the first game, it also includes some levels in the side-scrolling camera angle that would be used in later games in the series. Additionally, this game also includes a weapon upgrade system, with enemies dropping power-ups for multiple different weapon types. Also, unlike other contemporary shooters, while the ship can only use one of its special weapons at a time, it can switch between them at will. The ship can also pick up weapon pods, called CLAWs, which rotate around the ship, increasing it's firepower, like the Options in the Gradius series (though they only fire normal shots), while the CLAWs can also block enemy shots like the Force from the R-Type series. Unlike the Force in the R-Type series the CLAWs cannot be launched like a weapon. Each CLAW power up adds one to the player's number of CLAWs, to a maximum of two.
This game was released first for Sharp's X68000 home computer systems in 1988, and then for the Sega Genesis the following year. The X68000 version included better voice samples (including some profanity), and improved graphics (including parallax scrolling and some transparency effects).
Thunder Force III
100 years after Thunder Force 1 & 2, the war between the ORN Empire and the Galactic Federation carries on. The ORN empire has installed cloaking devices on five of their planets, protecting their main base, and the bio-computer that controls their entire empire, ChaOs. Further, they've installed a massive defense grid called Cerebus, which can block any battle fleet from penetrating the cloaking field. Once again the Federation's only hope lies on a single starfighter, the FIRE LEO-03 Styx – which is small enough to slip through the Empire's defenses, destroy the cloaking devices, infiltrate the enemy headquarters, destroy ChaOs, and end the war once and for all.
Among the gameplay changes from Thunder Force II and III, the CLAWs have now become more like the Options from Gradius – rather than firing normal shots, they now fire the same type of shot that the active special weapon is. Plus, when the player picks up the CLAW power up, the ship automatically gets the maximum number of CLAWs. Additionally, when the character is hit, the rather than losing all of the special weapon upgrades they have, they instead only lose the active special weapon.
This is the first game in the Thunder Force series not to get a home computer release in Japan. Instead the game was released for the Genesis. A variant was also released for the arcade and the SNES, titled Thunder Force AC in the arcades, and as Thunder Spirits on the SNES (due to Sega holding the trademark for the Thunder Force name). Both versions re-did some of the levels from the Genesis version, as well as the graphics, while the Arcade version added some re-makes of levels from Thunder Force II.
Thunder Force IV
While the ORN Empire has been beaten, it is not wiped out. The remnants of the Empire's forces and it's allies have united to form the organization “Vios”, and have set out to seek revenge on the Galactic Federation. The Galactic Federation finds Vios' headquarters on the planet Aceria, amasses their forces and attacks, only to be repulsed. Once more, the Federation finds itself relying on its new model starfighter, the FIRE LEO-04 Rynex, to get through the planet's defenses and wipe out Fios, and save the Galactic Federation from destruction.
The fundamentals of the game have changed little from Thunder Force III, with a few refinements. The size of the stages extends above the top and bottom of the screen, allowing limited vertical scrolling in addition to the vertical scrolling. Also, the player is able to choose in what order to play the first four of the game's ten stages. At the game's halfway point a charge attack called the Thunder Sword is unlocked. The player is able to perform the attack after it's unlocked only when he has the CLAWs. The game also had a limited Co-Op option – with two controllers connected to the system, the first controller directed the craft and controlled its speed, the second fired and switched weapons. This is the first game in the series to originally released on only one platform – the Sega Genesis.
Thunder Force V
Following the conclusion of Thunder Force IV, the FIRE LEO-04's pilots were forced to eject after the destruction of Aceria damaged the ship. However, the Rynex was not destroyed. Instead it floated, adrift in space, until it reached Earth in the year 2106. The ship increased human technological development by leaps and bounds, thanks to the AI Supercomputer Guardian, which was designed to help Humans reverse engineer the ship, and then exploit the technology to allow Humanity to expand out into the universe. However, Guardian had gone (essentially) rampant. The fleet of ships that it was designing were actually intended to be warships. Once the fleet was completed, Guardian set out on its ultimate purpose – exterminating humanity. The Rynex had been contaminated by the reminiscent of ChaOs, which had backed themselves up within it's computers, which were in turn transferred into Guardian. Now, humanity's only hope lies with the pilot of the most powerful starfighter not under Guardian's control, the RVR-02 Vambrace.
As this is the first game in the series to be released for disk systems (the Saturn and the PlayStation), the game uses polygonal graphics for the ships and enemies, as well as 3D graphics in the background, despite the 3D scrolling, making it a 2.5D game. As a consequence of this, the environments lack the limited vertical scrolling of the levels of Thunder Force IV. Also, rather than picking up power-up enhancements for the ship's weapons, the weapons are automatically enhanced as the character goes through the game. The game also includes as an Easter egg a several references to various bands, with bosses named after Iron Maiden, Deep Purple, and Alabama 3.
The ship can also carry an additional CLAW, now called a CRAW, bringing it to a total of 3. The CRAWs remain on screen when the ship is destroyed, giving the player an opportunity to recover them. The ship can also super-charge it's weapon attacks using the “Over Weapon” mechanic, by overloading the CRAWs. The game was released for the Saturn and the PlayStation, with the Saturn version having some enhanced graphical effects, and the PlayStation version adds extra art in the art gallery and CGI cut-scenes. This was the final game in the series to be developed by Technosoft, which closed it's doors in 2001.
Thunder Force VI
Ten years after the events of the Thunder Force V the last remnants of the ORN Empire, calling themselves ORN Faust come to Earth and overcome it's defenses. In desperation, the Unified Earth Government accesses the databanks of Guardian in an attempt to find a counter to this onslaught. Using the information from the Galactic Federation and the remnants of ChaOs, the Unified Earth government produces the RVR-00 Phoenix, humanity's last hope for survival.
The game was only released in Japan for the PlayStation 2. The player started out flying the Phoenix, and unlocks the Rynex-R and the Syrinx in subsequent playthroughs. The Phoenix and Syrinx don't lose any of their special weapons when they are hit, while the Rynex loses the active weapon. The game was released in 2008, and was developed and published by Sega.