Australian researchers recently announced that they have developed the world's smallest submarine. The designer said that this submarine can not only perform various deep-sea exploration tasks, such as finding mineral resources and sinking ships, but also has military uses. This 40 cm long toy-sized submarine is called "seraphine" and has automatic control function. Before entering the water, the designer set up an application program for it in advance, so it can automatically complete all scientific research work and return to the surface automatically after entering the water. Submarines can dive to a depth of 5000 meters and travel at a speed of one meter per second, which is equivalent to the speed of people walking. It can move freely underwater, not only turning and tumbling, but also hovering, sideways and automatically adjusting its position in the water. The submarine hull is made of plastic and has five propellers and rechargeable batteries. Youwei Zimmer, the chief designer of the mini submarine, said that the cost of this submarine is very low, and the cost is only about 700 US dollars. But its performance is very good, because of its small size and better pressure resistance than large submarines. Designers worry that this small submarine may be eaten as food by large marine life. The only nuclear-powered research submarine "NR- 1" of the US Navy is the smallest nuclear-powered ship in the world. Until recently, it was a highly confidential technology during the Cold War, mainly responsible for national defense and emergency civilian tasks, such as searching the seabed for the O-ring that crashed the space shuttle Challenger.

NR- 1, with a cost of US$ 98.7 million, was built by the Electric Shipyard of General Electric Company, and was launched at the beginning of 1969. It is a small nuclear-powered marine engineering research submarine with deep-sea observation and operation capabilities. It has a displacement of 400 tons and a total length of 4 1.8 meters. The center of the hull is a cylindrical pressure-resistant shell made of HY-80 high-strength steel, and the front and rear are non-pressure-resistant plastic shells. The pressure shell is about 30 meters long, and the front 1/3 is the control, observation and living area. The observation area is below the front console, and there are several observation windows at the front end of the pressure shell. There are five beds in the residential area, and the crew consists of two officers, three non-commissioned officers and two scientists. The rear 2/3 is the engine room, which is used to accommodate the PWR and the turbine generator, and the turbine generator drives the two electric propellers in the rear. Four grooved tube propellers (two horizontal and two vertical) control the submarine to perform precise underwater maneuvers.