Why a task group is more than its individual ships

Does a Type 45 contribute anything to anti-submarine warfare without a specialist towed-array sonar?

Yes. Its helicopter becomes part of a wider ASW system when cued by specialist frigates and supported by other task-group aircraft and submarines.

The answer rejects judging a warship only by equipment physically fitted to its hull. A Type 45's helicopter remains an anti-submarine asset even though the destroyer lacks a specialist towed array. Frigate sonar can cue helicopters carried by destroyers and carriers, allowing the group to investigate many contacts beyond the frigates' own embarked aircraft. A submarine operating ahead adds another hunting layer, while point-defense weapons on other escorts also contribute to air defense. The task group's capability therefore emerges from sensors, weapons, and aircraft cooperating across platforms.