However, the Marines and some advanced pirate crews/alliances commute daily between the oceans. To be more specific, here are a few examples to demonstrate what I mean:
The Marines travels between every oceans they want. By using Seastone on their ships, they can easily travel through the Calm Belt and switch between the Grand Line/New World and all Blues. Because the Marines is a member of the World Government, they can also pass the Red Line via Mary Joa.
However, the Seastone technique (Episode 410) is a new invention from Dr. Vegapunk. How did the Marines travel through the Calm Belt so easy before that? Another example in episode 502-503: How did a World Government ship travel from the Grand Line to East Blue 10 years ago when Seastone technique hadn't been invented?
Same for Whitebeard. One time, Whitebead was in the Grand Line, then in the East Blue, and then again in the Grand Line, etc.
How do Shanks and Whitebeard manage to travel between the Grand Line and the Blues on daily basis? Do Whitebead, Shanks and other Pirates also use Seastone like the Marines?
So I hope you see what my question is. I'm especially curious about the daily switching between the Grand Line/New World and Blues. As I know, the only way to enter the Grand Line is via the Reverse Mountain, which isn't the most harmless way as you can see in episode 61. Does that mean that every time Whitebeard and Shanks want to go to the Grand Line, they have to pass this small river with their gigantic ships?