Note that the following Steamship times are very approximate. There are a number of ports of call on most voyages, with stops varying from 2 hours to over 24 hours.
Throughout the 1920s White Star Line run a weekly service between New York and Southampton via Cherbourg, using the RMS Homeric, RMS Majestic and RMS Olympic in rotation. Departure from New York is Noon Saturday, Departure from Southampton Noon Wednesday. Journey time is usually 7 days. Many other services are also available.
The Steamship route is from Southampton to Port Said via Malta or Gibraltar/Tangiers. This takes about 10 days. However, an alternative is the Orient Express which can transport travellers in luxury from London to Cairo in 7 days.
Regular steamship services leave Port Said which can be reached from Cairo by rail in about 3 hours. Sea journey is via Aden (usually with a day's stop) and takes about 10 days.
There are a number of possible routes, with many going via Aden (which is 5 days from Mombasa by sea). However, the fastest route is direct from Mombasa to Singapore, and then on to Hong Hong and Shanghai. Time to Hong Kong is 17 days, total time to Shanghai after an overnight in Hong Kong is 20 days.
This journey is clearly very dependent on where in Australia one wants to go. The journey to Fremantle (Perth) via Aden is 21 days. From there it is a further:
6 days Perth to Melbourne
2 days Melbourne to Sydney
2 days Sydney to Brisbane
The sea journey from Mombasa to New York via Aden, Port Said, Alexandria, Naples and Genoa takes 31 days. This can be shortened by taking the Orient/Taurus Express from Cairo to England rather than carrying out the whole trip be sea. In this case it takes about 24 days.
The shortest route is to leave from the opposite side of the USA, i.e San Francisco, via Honolulu, Yokohama, and Kobe. This journey takes 20 days. A further 5 days is needed for the train journey from Boston to San Francisco, giving a total 25 days. (avoiding the train, and taking ship for the whole journey, via Havana and Panama, would add a further 13 days!)
The shortest route is to leave from San Francisco, via Honolulu, Pago, Suva and Auckland. This journey takes 20 days to arrive in Sydney. A Further 5 days is needed for the train journey from Boston to San Francisco, giving a total 25 days. Other Australian destinations will take longer, see Mombasa to Australia above.
12 days to Darwin via Hong Kong (taking 2 days) and Manila. 22 days to Brisbane via Hong Kong, Manila, and Rabaul. See above for other Austalian destinations.
Journey from Port Said via Colombo, Singapore and Hong Kong takes 20 days.
The route from Port Said via Aden and Colombo to Fremantle (Perth) takes 21 days. See above for other Austalian destinations.
This route is a combination of London to Cairo and Port Said to Mombasa. Total 17 days assuming use of the Orient Express.
The quickest route is a combination of London to Cairo and Port Said to Shanghai. Total 30 days. If travellers wish to take the whole trip as a single sea voyage, this can also be done from Southampton to Port Said via Gibraltar, Marseilles for a total of 35 days.
The quickest route is a combination of London to Cairo and Port Said to Australia. Total 28 days to Fremantle. Alternatively one can take ship from Southampton for a total 30 days journey via Gibraltar and Port Said