The Spartans of the Astartes

After the battle of Chi Ceti IV, the Covenant Ship explodes and creates a Warp rift that drags in the UNSC Commonwealth. The Commonwealth then crashes on an Imperial planet infested with Orks. The Spartans being the only survivors are rescued from certain doom by the Deathwatch and the males, having impressed the Watch Captain are recruited into the Adeptus Astartes.