yeah, you research it in the civilian tree (the last tec for them) 8 civic bases needed.
Then there should be an option in the phase lane box when you click on it (left hand side) for Dark Armarda.
However to call them you need about 1800 credits, 300 metal/500 crystal (at level 2) (don't know the exact number of resources you need off my head, just an estimate.)
However you also need about 150 (again, a rough estimate) Anti-Matter and it has a cool down waiting period of 5 minutes.
Failing that you can put it on Autocast so that they will appear at the phase gate planet gravity well you have activated it.
The Dark Armada (which is an assortment of random ships you can build in game aka enforcer/subvertor/strike craft carriers etc - not some specialist unseen fleet) will then appear at the edge of your planets gravity well.
(If you are unsure i would reccomend testing it on a planet where you have no fleet and an open space, therefore you will know any ships that appear will be from your dark armada).
Hope this helps.
If you need anything else don't hesistate to ask.
