Why early submarines sailed with destroyer escorts

Why did the submarine flotilla include destroyers?

Because early submarines traveled on the surface so often, destroyers escorted them to their assigned operating areas.

A viewer notices destroyers assigned to the submarine flotilla in the British order of battle. Early submarines traveled on the surface for much of their passage. Destroyers could escort them through exposed waters, help keep the formation together, and ensure they reached the positions from which they would operate independently. The arrangement reflects the limited endurance, communications, and surface vulnerability of early submarines. It also explains why the 1915 British force combined nominally separate ship types in one operational plan.