As HMS Juno was only an old protected cruiser with no anti-submarine capability whatever she was probably sent out of the area as she was only another target. Cruisers of this type could only defend against surface ships and needed destryoers as an anti-submarine escort.

The Admiralty would have been only too aware of what had happened to the armoured cruisers Aboukir, Cressy and Hogue some time before. After one of them was torpedoed and was sinking the others stopped to pick up survivors and were sunk in turn. Which is why Juno was not sent to pick up survivors from Lusitania.