I used this as a reference. It gave me the general idea and layout of a PT boat (which obviously I didn't put in all the details) So the obvious first step to take was create the body of the ship by stretching the cube you start out with to the approximate height and width.
Something to note about the PT boat is that on top of the body, rather than concaving like a normal boat you may see, it convexes. Shaping up the body is pretty easy, and I only need to do a loopcut twice. The scale tool comes in handy when doing the bottom of the ship and also the front. No extruding is needed until the cylinders, which are two completely different objects.
For the cylinders, I simply scaled them on the z axis and then extruded the edges. After I placed the cylinders in their correct places, I joined the objects.
The last part of this project was the torpedoes, which was simple enough. I scaled down the object as a whole until I achieved the radial size I wanted and then made it longer length-wise. Back in edit mode all I had to do was select the center and then pull it outward. A quick note: as a cylinder, there are many vertices that meet on the front and back face, to make sure you select them all, hit C to use the circle select, and select the middle (make sure you are using the vertex select) you can use the middle mouse button to change the size of the circle select. Right click finish using the circle select.
The PT boat as a whole is actually 8 objects joined together; 4 torpedoes, two other cylinders, the base, and the mesh on top of the base. Overall it took about 30 minutes. Tomorrow there will be a second explanation on exporting the object and also how to fix it if the faces are turned inside out.