I've been reading Persian Fire by Tom Holland, and followed it up with Donald Kagans Peloponnesian War.
As of Darius' invasion of Greece, Athens had a minimal naval power. Politicians like Themistocles realised how important a strong navy would be in the impending second Greco Persian war, and made efforts to build the Athenian navy which eventually won Salamis.
However, less than 50 years later, Athens was so vastly powerful at sea that during the Peloponnesian war, it seems like people would shy well away from even a hugely outnimbered Athenian fleet. Athens used to frequently dive into naval battles with numerical inferiority and totally clean up.
My question is, what extroardinary measures led to this turnaround? 50 years does not seem like a long time to go from having zero ships to being a naval superpower.
I'm not familiar with the history of Greece, but I can assure you 50 years is a long time. Let me explain futher:
I'd argue that the US Navy's actual birth was in the very early 1900s when Roosevelt started to heavily invest in it. I'm not saying the US Navy was weak before 1900, but they definitely weren't the top.
From 1900 to some time during WWII, the British were absolutely dominating the sea until the Germans came into play and the Americans entered the Pacific Theater. Then, starting from the Cold War, the Americans are the true superpowers of the sea.
50 years is enough time for the position of naval superiority to be passed around.