Scramble

The 1981 Arcade Game Scramble was Konami's original Horizontal Scrolling Shooter; it was one of the first games in the genre, along with SNK's Vanguard.

The player flies a jet fighter armed with lasers and bombs to fire at enemy rockets and flying saucers, trying to avoid colliding with them or the terrain. Hitting fuel tanks not only scores a few points, but replenishes your ever-dwindling fuel supply. After five levels, the player flies into the base of the enemy system and destroys a target, after which the game loops with higher difficulty.

A sequel, Super Cobra, was released the same year, with the player now in control of a helicopter and carrying away a suitcase at the end instead of bombing a target. There were now ten levels before the base, and the garishly colored backgrounds were slightly more textured, but otherwise, the arcade versions of Scramble and Super Cobra looked and played pretty much the same.

Super Cobra was ported more widely than Scramble in the 1980's, but Scramble has since turned up more frequently on Compilation Rereleases of Konami's older games, including remade versions on the Game Boy Advance and Xbox Live Arcade.

Scramble was retconned into the Gradius series in Gradius Generations. While it doesn't fit into the Gradius continuity (since it has no real plot), its influence on Konami's later games is obvious.

Tropes used in Scramble include:

Airstrike Impossible: The objective at the end of Scramble.
Deadly Walls: Avoid running into buildings or hills. However, once you bomb the base in Scramble, you can sacrifice your ship and get a free replacement when the game starts over.
Direct Continuous Levels: Scramble is probably the Trope Maker for continous-scrolling shooters. The end of each level opens up onto a piece of flat terrain, a short message is displayed with an accompanying jingle, and then the next level scrolls into view.
Endless Game: Once you bomb the base (Scramble) or steal the booty (Super Cobra), the game starts over with a faster fuel consumption rate.
Every Ten Thousand Points: Both games grant you an extra life every 10,000 points.
Trope Maker: First game that could legitimately be called a "side scroller".