In Minecraft, one of the most versatile blocks is the block of obsidian. Not only is obsidian extremely strong and resistant to explosions, but it's also very easy to mine. This makes it the perfect choice for building a tank.
To build a tank out of obsidian, you'll need at least 12 blocks of obsidian (more if you want a larger tank). Start by creating a 3x3 square of obsidian blocks, with one block in the middle missing. Then, place another layer of obsidian on top of the first layer, making sure that the middle block is still missing. Repeat this process until you have reach the desired height of your tank.
Now it's time to add some water. Fill up your tank with water by right-clicking on each side with a water bucket. Once your tank is full, stand back and admire your handiwork!