The double hull was a long way ahead of its time and only came into sharp focus with the sinking of the Titanic over 100 years later.
After the Titanic sank her sister ships were fitted with double hulls, the Olympic had to be retro fit as she was already in service but the Britannic, which hadn’t been started was redesigned to include the double hull, thus making her the largest of the Olympic class.
The double hull didn’t save the Britannic when she was torpedoed in fact some engineers believe that the double hull contributed to her rolling over and sinking so fast.
The double hull would have saved the Titanic from sinking due to the damage caused by the gash in her side, but would have been inefective to help with the missing section of the ships bottom.
Paul