T'Kuvma didn't cloak his ship
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The *Europa* was rammed by a different ship under T'Kuvma's command, which was already cloaked.

This had been my impression watching the episode, but as evidence I'll submit the following:

 - The [StarTrek.com database entry for Admiral Anderson][1] leaves the attacking Klingon ship unnamed, despite having [a separate entry][2] for T'Kuvma's flagship:

   >Starfleet Admiral at the Battle at the Binary Stars. He was killed when a Klingon cleeve ship attacked the *U.S.S. Europa.*

 - The Klingon ship appears atomized after the *Europa* self-destructs, but T'Kuvma's flagship is completely intact after this; there's no evidence of damage until the *Shenzhou* fires on it a few minutes later

  [1]: http://www.startrek.com/database_article/admiralanderson
  [2]: http://www.startrek.com/database_article/sarcophagus