Britain used its supremacy at sea to build and maintain its empire between 1800 and 1914. Britain conscripted sailors from its colonies, much to the chagrin of the United States, in the buildup to the War of 1812. Britain insisted on creating the strongest navy in the world and spent large sums of money to ensure that it had this. Other than the Crimean War, Britain largely stayed out of wars in Europe, thus allowing it to focus more on its naval strength. Britain built the Suez Canal in order to provide a fast route to its prized colony of India, and it maintained colonies in the Pacific, such as Singapore. British colonies all over the world would be especially important as ships transitioned to steam power, as there was a constant need for new coaling stations for battleships. When Germany began its naval armament program under Kaiser Wilhelm II, Britain increased its own number and size of battleships. The idea was that a large battleship fleet would keep Britain at peace with rivals in Europe. This naval arms race was quite expensive, but pride in the battleship fleet was also a source of nationalism for many imperialistic British citizens before World War I.

The British Empire was very much dependent on maritime trade because of the fact that Britain is an island and the fact that so much of its empire was so far away.  Therefore, it had a strong interest in protecting its trade routes.  It did this in two major ways.

First, it maintained a very strong navy.  Britain had the strongest navy in the world from at least the 1600s until WWII.  Britain was constantly working to make sure it kept this advantage, as with the creation of the Dreadnoughtclass of battleships that were created to make sure the Royal Navy remained superior to Germany's navy.

Second, the British took control of strategic areas on the land.  The most important example of this was northeast Africa.  Soon after the Suez Canal opened, Britain realized its strategic importance.  Therefore, Britain soon came to dominate the area of Egypt and Sudan that control access to the Suez Canal.  

In this way, Britain protected trade routes both by land and by sea.