What is submarine capital of the world?

There is no specific city or location that is officially known as the submarine capital of the world. However, there are several cities and locations around the world that are known for their submarine technology and manufacturing capabilities. Some of these locations include:

1. Groton, Connecticut, USA: Groton is home to the United States Navy's primary submarine base and the General Dynamics Electric Boat shipyard, which designs and builds submarines.

2. Kiel, Germany: Kiel is known for its U-boat heritage and is home to the German Navy's submarine fleet. It is also home to ThyssenKrupp Marine Systems, which manufactures submarines.

3. Portsmouth, United Kingdom: Portsmouth is home to the Royal Navy's submarine base and the BAE Systems shipyard, which builds submarines.

4. Saint-Nazaire, France: Saint-Nazaire is home to the Naval Group shipyard, one of the largest manufacturers of submarines in the world.

5. Visakhapatnam, India: Visakhapatnam is home to India's first nuclear submarine, INS Arihant, and is a hub for submarine development and technology.

Overall, these cities and locations showcase the expertise and innovation that goes into creating some of the most advanced submarines in the world.