Thunder Force is the first installment in the series of the same name. Created by Tecno Soft (or Technosoft in the U.S.) in 1983. It was released originally for the Sharp X1 computer, and later appeared on the Sharp MZ-1500, NEC PC-6001 MK II, and in 1985 on the NEC PC-8801 MKII. In 1984 was released on the FM-7 and NEC PC-9801 computers as Thunder Force Construction, featuring an add-on that allowed players to create their own areas.
The ORN Empire has built a large asteroid fortress named the Dyradeizer to oppose the Galaxy Federation. In addition to its high firepower capabilities, Dyradeizer is supported by shield generators hidden in various locations by ORN, which render the fortress invisible. In an attempt to destroy Dyradeizer, the Galaxy Federation sends their specially designed fighter, the Fire LEO, to locate and destroy the shield generators and defeat Dyradeizer.
The structure of the game consists of overhead, free-directional scrolling areas and the player's ship is armed with main shot to shoot airborne targets and a bomb shot to shoot ground enemies. Gameplay consists of flying the Fire LEO over ORN occupied areas while destroying enemy base installations and turrets. Each area has a certain number of shield generators hidden under the ground based enemy targets; in order for an area to be completed, the shield generators must be found and destroyed. After doing so, the Dyradeizer will temporally appear and the player must destroy a certain section of it. Once this section is destroyed, the Dyradeizer will disappear and the player will be taken to the next area to repeat the process.
Graphic and sound wise, Thunder Force is very crude and modest compared to its successors, and is considered the most obscure game of the series (at least from a non-Japanese perspective).