Between the 10 and 14 April, you can do some special missions that get you premium days and a free Chi-Nu Kai (but you have to work hard to get it):
Happy Anniversary (Part 1)
Fullfill all the conditions in the following number of battles: 15
- Win a battle
- Be among the top 10 players on your team by the following parameters: Experience earned Reward: Premium days: 1; unlock Part 2
Part 2:
Experience earned: 75k
In each battle: Be among the top 10 players on your team by the following parameters: Experience earned
Reward: Premium days: 1, unlock Part 3
Part 3:
Fullfill all the conditions in the following number of battles: 30
- Be among the top 10 players on your team by the following parameters: Experience earned
Reward: Premium days: 1; unlock Three Cheers
Three Cheers for World of Tanks:
- Win a battle
Reward: Slots in the garage: 1, Type 3 Chi-Nu Kai (50% crew)
Guess who’s playing japanese mediums. 🙂 Well, i guess everyone will be sooner rather than later.
tl;dr courtesy of redditor mechanicalgod:
Part 1: Win 15 battles (finishing in the top ten)
Part 2: Earn 75k XP (finishing in the top ten)
Part 3: Play 30 battles (finishing in the top ten)
Part 4: Win a single battle
Part 5: Get Chi-Nu Kai
Can be done in any tank.