None. You will need to buy one of the Pre-Order packs to get into the CBT now.
If you want the USS Arkansas, you will not want to wait around too long. In roughly a week, they will announce the OBT date, though it will likely be at least a couple of months after before it hits. Fortunately you will only need 49 battles in either Co-Op Battles or Random Battles, or a combination of the two to get her. You will get her when it goes OBT.
I'm sitting on 300+ Co-Op Battles and 65 Random Battles, so I will get her come OBT.

As a heads up, when OBT hits, EVERYTHING is wiped. The only premium ships that will remain after the wipe will be the 3 Pre-Order pack ships, the Alpha Iwaki (for those who were lucky enough to get into Alpha) and the Beta USS Arkansas. Any prem time and gold you get as well, will be refunded in full upon launch.
The 3 Pre-Order ships will remain exclusive to those who got it for a full year after full release. The Alpha Iwaki and Beta USS Arkansas will NOT be made available at a later date.