How would a larger and more powerful navy contribute to national greatness? Who contributed most to this idea?

Alfred Thayer Mahan

Explanation:

The Navy, now and in the past, can contribute to national greatness because it enables the country to fight and attempt to control the seas. With 71% of the Earth covered by water, this is a significant thing to control.

And even when the nation does not need the navy for fighting, it can employ it to help in trade. Even with planes and rail, the ocean remains the major conduit for trade so a larger and more powerful navy can protect and encourage a nation's trade thereby making it richer.

This combination of military and commercial use is what saw the British Empire establish itself as the largest empire to ever exist.

This idea was contributed to and expounded upon more famously by the American navel officer and Historian, Alfred T. Mahan who's books on the subject were very influential in the late 19th and early 20th centuries