Allies
Ship Allies are unique artifacts that can join your ship similar to the way a crew member would, however each one must be acquired through missions or another source. Each Ally requires 0 deck and has different bonuses depending on their type and rank, typically starting with 2 stats at rank 1 and increasing to 5 stats at rank 100. An ally will typically gain a new attribute or stat at Rank 30, 60, and 100.
It was originally believed that each ship was only able to equip two allies, but as of October 15th 2012, the text that said, 'Limit 2 per Ship' was removed along with the restriction, and you can have more than two allies.