How to get a new sub?

[Soterius]

So when do you get rewarded a new sub? Do you get one new sub for every year or is it influenced by renown or does it just happen randomly??? I searched the forum for an answer but couldn't find it. I did read someone saying he got a better sub after his old one was too damaged...should I just keep damaging my subs so I can get a better one??? How does this all work?

Thanks in advance!