The idea of the tank has been by-passed by air-technology since the end of W.W. II. During W.W. II the anti-tank role of the airforce increased considerably and made armoured warfare a hazardous undertaking. I think that the helicopter has taken over the role of the tank and APC, because it is much faster and has no difficulty crossing the terrain. It is also important that helicopters can be more easily supplied than tanks. Helicopters only need safe havens, but can also operate from vessels, making a landing on a beach more easy, especially on swampy beaches. They also provide immediate heavy fire-support to infantry. More speed and less sound are key factors of modern warfare, because of the changes of warfare. A quick, swift and unexpected strike on targets well inland, which cause disruption and chaos will cause more effect. I think that in the 21st century frontlines will disappear and war will be limited to hunting groups who will fight for key locations and installations. Maybe war will rage within certain squares/hexes and not along lines. This kind of change will need diffirent kind of weapons and means of transportation, notibly from the air. The helicopter has both speed and flexibility which tracked vehicles, which are bound to the ground, have not.