Why did cruisers carry depth charges?

How effective were depth charges on cruisers in the Second World War?

They were common because cruisers could be asked to perform anti-submarine work, even though ASW was only one secondary role among many.

Depth charges were surprisingly common on Second World War cruisers. Their presence reflects recurring proposals to give cruisers sonar, ASDIC, and some anti-submarine capability. A cruiser was not necessarily the ideal submarine hunter, but independent operations could put it in waters where no specialized escort was available. The equipment therefore illustrates how the broad cruising role pulled ships toward secondary missions beyond gunnery.