Tutorials/Igniting TNT underwater

Making TNT explode underwater seems impossible, especially if you're not using the Education Edition. However, with this special technique, you can create explosions even though you're in water!

Materials needed

 * 1 sand, gravel
 * TNT
 * a flint and steel or fire charge
 * any kind of building block, but not too expensive (recommended, to reduce the fail chance)

Steps

 * 1) Find any body of water. It could be a lake, river, or in the middle of an ocean.
 * 2) Place the TNT block, with a block of sand or gravel on top.
 * 3) Ignite the TNT with your flint and steel then step back and watch the magic happen. (Note that the TNT would move slightly when it's ignited, hence a few blocks are needed to prevent it from happening.)

Explanation
The reason that this works is that the TNT does not actually explode inside water, but inside the sand/gravel block. When the TNT is ignited, it becomes an entity, meaning another block such as sand or gravel can fall in and occupy its space. Normally when a TNT explodes underwater, the high blast resistance of water shields adjacent blocks from explosion, But when it explodes inside sand or gravel which has a low blast resistance, the explosion is no longer shielded and can destroy adjacent blocks. This phenomenon was reported as, but was resolved as "Works As Intended", meaning it is an intended game mechanic that doesn't exploit any glitches.

Video tutorials
OMGCraft's design:

A more expensive, but simpler, method
Surround the TNT by blocks with low blast resistance, or dig a one-block hole in the ground and place the TNT inside, so that no sides of the block, except the top side, touch water. Then cover the top of the TNT with a redstone block to activate it. Redstone block was chosen because it is the only source of redstone signal to function underwater, not counting the USB Charger Block.

教程/在水下利用TNT破坏方块