Graham McNeill
Chains of Command

Uriel Ventris is a warrior who fights every battle according to the Codex Astartes. When a mission to destroy a vital bridge goes wrong, he must quickly learn to work outside of the codes and rely on his own initiative.
Warhammer 40k
short

Also in:
Ultramarines: Quick Reads Collection
The Uriel Ventris Chronicles: Volume 1
Honour And Vengeance: Uriel Ventris Vs Honsou
The Hammer And the Eagle: the Icons of the Warhammer Worlds