Congrats to the Royal Navy for naming their new Submarines after the Dreadnought. If you don't know why that is cool - google it (Battle of Trafalgar)! This design is intended for pool or beach use, Product features include: 3 part construction of main hull. sized for a Lulzbot Mini-printer. Each end of the hull parts is specially designed to hold onto heated beds but not too much! the parts are easily joined with hot glue. The sub can be printed hollow and gravel or marbles can be added as ballast. Print the hull solid and add buoyancy to achieve the best performance for your kiddies. We printed it hollow and added ballast in the form of beach sand. after it settles it makes good ballast and can be shaken out to make it more buoyant. Gravel works best because it will not escape through the 3mm vent holes. A screw cap makes adding ballast easy and allows for faster drainage. Tie a string through the cap and the hull to keep it from being lost. We suggest printing this from vibrant materials so that it is easier to see in the water. Diving into this thing would hurt - loosing a black sub at the beach would be very easy. The rear fins could hurt little feet if dropped on them - keep this in mind especially when the submarine is full of ballast. See below for more model details about this genuine STLhive.com part.