Posted: 07/28/08 A cat and mouse battle between two submarines using sound waves to see.

This idea is an old one and I figured it was about time I bothered to write it down. The idea itself is not particularly original (not if you've seen Das Boot) in that it is essentially two submarines trying to locate and destroy each other - but first they must find each other using sonar. This idea revolves more around the concept of using sonar as a gameplay device and how to visually represent it.

There are two submarines on a fairly large 2D map. The submarines have the sort of classic operations - dive too deep and the hull starts to collapse. Use torpedoes to hit those on the same basic level, depth charges to hit those below, and missiles from the top to hit those above. If they hit the walls or floor, they are damaged (perhaps even destroyed). They move slowly, and dive/rise even slower.

The twist is that the submarines "see" through the use of sonar. They bounce sound waves (pings) off the environment and each other to realize their surroundings. Anything that makes sound can be "seen". This creates very limited vision since quiet things or obscure things are effectively invisible.

There are two basic ways to use sonar in this mechanic. The first is a sort of visual bubble around the sub. It sort of represents the basic noise level that a non-hidden ship makes and how it is reflected off the immediate environment. Using this, you can see in a small area around your ship. Of course, you can see, but you can also be seen. By going into silent running, this bubble goes away and you are stuck in total darkness. You can still move around, but you risk hitting a wall. This sound bubble can exist in large, small, intermittent, and off.

The second way to use sonar is to send out an active ping. This is simply a sound wave which moves in a specific direction and bounces off the environment, illuminating where it bounces. Pings are safer than the sound bubble since hitting the other submarine will alert it that it has been pinged, but it can not trace the ping back to you. They can only see the surface it was immediately bounced off. In other words, they know they've been seen, but not from where unless they send a ping back.

As the illustration shows, it does not give a complete picture. Jagged edges are far more difficult to see - there are several areas which could contain spikes that would damage your ship. Though it is safer concerning the other submarine, the picture of the environment you get is incomplete. Also, the bouncing may be difficult to predict (and you probably don't want to send it directly towards the enemy since you would be the last surface and they'd see you). Also, since pings bounce, hiding behind the terrain is a good way to stay invisible.

Also, this illustration is not the best since it shows the path a ping travels, but each one of these illuminated walls would be lit up in sequence and start fading out. The idea is that they are echoes of where the objects where when they were hit. If the objects were moving, they may already been somewhere else by the time you get there. The entire world is seen through fits and starts and it is up to you to fill in the blanks.

I think as written, this provides a fairly nifty competitive experience, but there's a lot of things I could think to add to the game. For instance, the ability to fire "ping mines" - things that sit on a wall sending out pings, allowing you to see in a small around around them (and you can lock them to the opponent submarine). Maybe sea life, like whales, or inflatable decoys, which can be mistaken for the enemy sub. Perhaps the ability to deform the terrain with explosions, creating the possibility of subs creating new paths or hiding in newly created craters.

One idea I sort of like is each player having a hidden base somewhere in the level. Maybe they can find elements out in the world and bring it back to the base to upgrade their sub and research new tools. I think it'd be cool to be able to go in your opponent's base and battle him hand to hand in his command center.