4. HALO Reach
Oh, Reach. The big tragic moment of the Halo saga. Even before the game started, fans of the series knew this would not end well. And so with the progressing game, more and more members of Noble Squad got offed. One Spartan at the time until only Noble Six is left.
The important thing Noble Squad had to do was ensuring Cortana’s survival, and then ensuring the Pillar of Autumn’s safe launch. The squad itself was expendable, especially since the Covenant was winning the attack on Reach, each mission essentially being a losing battle, fought back against the wall.