The light cruisers are sent close enough to hold the French in action. They are explicitly called sacrificial because their purpose is to stop the enemy from running away. That creates time for the heavier force to destroy separate French elements. The action carries a clear cost: a weaker unit is put at risk to secure the larger operational result, and one light cruiser is lost.
Notable Point · 51:27-51:54
Sacrificial cruisers fix the enemy for destruction
Light cruisers serve as sacrificial fixing forces so the slower battle line can prevent a French withdrawal and destroy the fleet in detail.