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Specialist detachments technically still exist, but they aren't legal to use in GT2021 missions, so aren't really used anymore.

Specialist detachments are still allowed in Eternal War missions, but those are generally seen as just inferior version of the GT missions, and so aren't commonly played.
They 'might' still work in crusade games, although I'm a little fuzzy on how crusade interacts with specialist detachment relics.]]> http://www.dakkadakka.com/dakkaforum/posts/preList/802699/11278876.page http://www.dakkadakka.com/dakkaforum/posts/preList/802699/11278876.page GMT
It's Cadian only, and a relic for a TC with Battlecannon.]]> http://www.dakkadakka.com/dakkaforum/posts/preList/802699/11278897.page http://www.dakkadakka.com/dakkaforum/posts/preList/802699/11278897.page GMT http://www.dakkadakka.com/dakkaforum/posts/preList/802699/11279311.page http://www.dakkadakka.com/dakkaforum/posts/preList/802699/11279311.page GMT