Here’s five things that could maybe help:
Broadly speaking, having a blue water navy means having the capacity to deploy a task force of ships across the open ocean, and to support them at great distance from their bases. Having a blue water navy means that a nation has the potential to play a big role on the international stage. Indeed, developing a blue water navy may be more complex, expensive, and useful than building a nuclear weapon.
In Mahan’s day, what countries needed to count as having a blue water navy was a series of coaling stations that they could access during war. This could mean colonies, friends, or a healthy set of financial accounts. Times have changed, but much of the basic logic of blue water deployment remains the same.