My question is two-fold:
How did Trafalgar Law and the other "Worst Generation" pirates get to Marineford? I thought you had to go through the tri-currents? Or is that the tri-currents are just a faster way but you can come any other way since Marineford is not in the calm belt?
How did Trafalgar Law leave the tri-currents? This especially puzzled me. I am thinking now that it might be because of their submarine. My assumption is that it can move freely, does not depend on currents, but I am not sure.
I would appreciate answers that are based on more than just speculation.