

You get through the fastest by having premium time, using xp boosting flags and camo, and by playing well. The RB points stay on the hull until you actually buy and play the boat (a win or 300 base xp gets the RB points credited). Sometimes I reset the line again before playing the T10. Anyway I normally play the ship all the way through to the next tier and then it's rinse and repeat until I've researched the T10. (for torpedo boats I typically don't bother with the gun range module).

I then use free xp to buy the modules and play the ship in that state.

When I reset a line I free xp up to T5 before I buy the boat. If you haven't noticed there are no more free xp boats, so RB is now where you spend that extra free xp. When you reset a line all the upgrades are put in inventory (so you don't need buy them again) and the captains go to the reserve. If you are going to reset a line a lot you can save a lot of time by having dedicated captains through the line so you don't need to retrain them over and over. I've reset the IJN torpedo line the most. I did this line because it's one of the cheapest to do, I enjoy it, and I have 19 point captains on the T6 and up. These days I just reset one line at a time. Anyway the point is I've reground a lot of lines. Battleships are the most expensive and take the most XP, I've done the French BB's a couple times and the US BB's once, but never again, it's too much work. I have all the RB ships but the last two. I also have 100K in RB points I just haven't decided which ship to get first. I am what scientists call a nut ball, when RB first came out I reset 6 lines at once.
