Final answer:
The success of Weltpolitik relied on a large navy to assert global influence, protect overseas interests, and compete with Britain's naval dominance. The development of Britain's Dreadnought battleship escalated the arms race, compelling Germany to expand its navy as a deterrent and to safeguard economic prosperity via trade and colonies.
Step-by-step explanation:
The success of Weltpolitik, Germany's aggressive foreign policy which aimed at transforming Germany into a global power, heavily relied on a large navy. A dominant naval force was vital for Germany to assert its influence and protect its overseas interests, especially in competition with Great Britain, the leading naval power at the time. The advent of the Dreadnought battleship by Britain in 1906, with superior speed and firepower, revolutionized naval warfare and prompted an arms race. Germany followed by building its own fleet but could never quite match Britain's numbers. The German strategy of building a stronger navy with modern submarines was also a response to the perceived encirclement (einkreisung) by Britain and its allies, leading to militarism and the subsequent arms race that heightened tensions prior to World War I.
Moreover, as Alfred Mahan's theories in The Influence of Sea Power upon History suggest, a strong navy was not just for war but crucial for protecting trade routes and ensuring economic prosperity by maintaining and acquiring colonies and naval bases worldwide. This reflects the era's broader belief that a powerful navy was essential to national greatness and survival in the competitive struggle among nations.