What is a water cannon?

Modern people have invented a new type of gun, which is different from traditional gunpowder. Its gunpowder is made of liquid.

1990, the general electric company of the United States conducted a shooting test on 155mm self-propelled Grenade water cannon. Unexpectedly, this kind of water cannon is much better than ordinary solid propellant cannon: it does not produce smoke and muzzle flame, and has good concealment, which can increase the muzzle velocity of the projectile 10% and enhance the power of the cannon. What is more prominent is that its shooting accuracy is very high. Of the six shells fired, they can hit a target at the same time within the range of 6 ~ 49 kilometers.