What do you think, was it small, like Mercies and Swords, or large, like Justices?
The author herself is not sure, but speculates that its size is intermediate between a Mercy and a Sword:
(Matt Gutting): @ann_leckie is there anywhere other than you I could go to answer this question? Don't have books with me. (9:48 AM - 7 Nov 2016)
(Ann Leckie): @matgutting I actually don't know for sure! I didn't need it for the books. That said, probably larger than a Mercy smaller than a Sword.