Officers (and presumably Marconi personnel) had gangway doors port & starboard under the wheelhouse.
First Class Entrance (for external gangways) two doors each port & starboard amidships leading to a vestibule
Second Class Entrance: two doors each port & starboard and a folding gangway door port & starboard, forward of the aft Well Deck
Second Class covered promenade: Two doors each port & starboard
Third Class, Forward Well Deck: Two folding gangways each port & starboard, one 14' (forward) and one 12'6" (aft). These were for single men. Engine crew may have also boarded here because the capacity is very high.
Third Class, Aft Well Deck: Two folding gangways each port & starboard, one 12' (forward) and one 10'6" (aft). These were for single women and families.
First Class: Two 4'5" x 6' doors each port & starboard leading to the Reception Room. This would have been used by passengers embarking or disembarking by tender.
Third Class: Open Space under Forward Well Deck, one door starboard only.
Third Class Permanent Section 'B': Doors port & starboard for single men embarking or disembarking by tender.
Second Class Entrance: One 4'5" x 6' door starboard for passengers embarking or disembarking by tender.
Third Class Section 'K': One 4'5" x 6' door starboard for single women and families embarking or disembarking by tender.
Crew: Port side only, door leading to working alleyway.
Store Entrances port & starboard, aft of the Second Class Entrance, for perishable foods boarded by tender. The entrances led to #4 Hatch, which was the normal means for loading food.
That should cover how all passengers got aboard. I also included the stores entrances since some perishables would have been procured from France or Ireland. I didn't include coaling ports. Note that the upper entrances were for use when the ship was docked alongside a pier or wharf and gangways were available. The lower doors were for passengers embarking by tender. Also, Third Class passengers were separated into either single men or families and single women. This separation was rigidly enforced and White Star was known for it. Women traveling alone in 1912 faced reality, not the genteel Edwardian society we think of today. There are several excellent accounts where women journalists described conditions in steerage for the immigrants coming to America. Sexual harassment was to be expected and rape was commonplace.
Some open questions:
- How did each type of crew member board, exactly? Crew would be officers and Marconi operators, deck crew, engine crew and victualling crew. They had separate quarters and the locations of those quarters were rigidly defined by tradition.
- What is the third class starboard-only gangway on D Deck for?
- For second and third class, passengers arriving by tender could only go by the starboard side (2nd class) or the port side (3rd class). Were the doors connecting the classes ever used (on Olympic) for passengers of the wrong class?
- How was baggage loaded for tendered passengers?