How to Make a Lego Submarine

Decide how big you want your submarine to be. Choose a flat Lego piece in the appropriate size. In order to measure Lego bricks, simply count the dots on the top of the bricks. For instance, a piece that is 4-by-6 units should have 4 dots across the short side and 6 dots across the long side. The submarine itself should be at least 4-by-6 units or 4-by-8 units, but it can be much bigger if you would like. Try to use only one piece, however. If you try to attach two or more flat pieces, it will be flimsy.

Create the bottom of the submarine first. Flip over the flat piece and line it entirely with 1-by-4 or 1-by-2 pieces. Make sure that they go all the way around so the entire bottom is lined with pieces.

Make another layer of 1-by-4 or 1-by-2 pieces, but this time, put the layer inside what you've already done. This layer should go all the way around the piece, but should be 2 Legos high. When you are finished, you will have what looks like the beginning of a pyramid.

Continue to add pieces in this manner until you have a submarine bottom that is entirely rounded. When you get down to a space that is 2-by-4 units, simply use a 2-by-4 brick to close it in. This will make the flat bottom of your submarine.

Flip the submarine over to begin to work on the top portion.

Put a windshield on the front. Also add any side windows you would like.

Add any Lego pieces that you desire to the inside of the submarine. They can include control panels, steering wheels or any other details.

Build the walls in the same way you built them underneath, but this time be mindful of the windows. You shouldn't need to use as many pieces for this. When you get a top that is 4-by-8, stop building the walls.

On the top, use a piece that is 4-by-8 but hinged so that it will open. If you don't have any hinged Legos, simply use a flat piece.

Add headlights, back lights and antennae to the outside of the submarine.