about the Olympic and uboat,there was one more thing they got.. in dry docks for inspections after collision i think they found one or two hull deformations suggesting there was unsucceful torpedo attack attempt too..
as for Olympic if he did collide with iceberg same way titanic did he would sink surely because same materials were used,also weak rivets! in case of britannic it was upgraded after titanic loss so if britannic hit iceberg in titanic style,it could have reached flood limit but not sink (britannic could stay motionless on water with 6 compartments flooded).
titanic had some opened portholes too but not as much as britannic but in final sinking stage they helped get water in quicker a little. that why port list ramped up because some portside cabins flooded while some starboard cabins didnt flood. anyway those opened portholes on titanic did not pay any key roles because there was only few opened.
