What game was this?

[Maximilian]

I only had the demo of it. Ill just say what i remember from it and hope someone knows what im talking about

Graphics
The graphics were 2Dish they looked 2D as in they were flat but they were pretty damn good for a 2D game. It looked like it was set in modern times or maybe a bit in the future, so tanks and army stuff were present.

Gameplay
You played as a guy and you walked from left to right (like a sonic game) to get to the end, you could shoot people and also take enemy vehicles, some were lying about. Im pretty sure you had to take the unmanned ones, you couldn't steal already occupied vehicles. There was a hidden yellow submarine within this demo that i found, it wasn't that well hidden but you had to swim to get to it.

Other notable stuff
Was developed and released around 2002-2004 time period, i don't know when exactly. I remember playing this on my new A64 3200+ with 9800 PRO, which i got around 2003ish, not that this game needed the horsepower.

 

[GaryJohnson]

Metal Slug 3? But it wasn't on PC.

Edit:
Correction. Metal Slug 5 also had the submarine and was on PC in 2003.

Edit #2:
Further correction. Metal Slug 5 was only on PC in Korea.

 

[Craig234]

There was a hidden yellow submarine

The Beatles made a game?

 

[Maximilian]

Metal Slug 3? But it wasn't on PC.

Edit:
Correction. Metal Slug 5 also had the submarine and was on PC in 2003.

Edit #2:
Further correction. Metal Slug 5 was only on PC in Korea.

Nah it wasent that, the game im thinking off looked much less arcadey, i remember thinking looked pretty advanced, the screen was pretty clutter free too.