Penetrator is an early Sinclair ZX Spectrum game made by Melbourne House programmer Philip Mitchell, one of the early hits. It was released in 1982 as a clone of the Scramble arcade game.
In Penetrator, the gamer flies a ship, which can shoot forwards and drop bombs beneath the ship. The first level is on open air, with just mountains to dodge, missiles which try to hit the ship, and animated radars. From the second level onwards, the game is inside increasingly complex caverns, so the ceiling is also a danger, as well as new enemies - the missiles are now sometimes replaced with skulls that can move up and down, blocking the path.
The levels change with no pause, only the screen colour changes. After four levels there is a short fifth level where a base needs to be destroyed by dropping a bomb precisely, and then there is a firework animation as a reward. After all levels are finished, the ship goes back through inversed levels, with backward turned landscape.
Source: Wikipedia, "Penetrator (computer game)" available under the CC-BY-SA License.