Hong Kong to Papua New Guinea 1940

I came across your site and am hopeful that someone may be able to assist, or if not, then possibly give me some ideas of where to go next?

My Chinese parents in law sailed from Hong Kong to Rabaul Papua New Guinea in either late 1939 or early 1940. I have been told that the name of the vessel was Thunder - although this was from an 8 year old. However as several of the children mentioned this name I believe it was named that or that the word Thunder formed part of the name.

I am wondering if there is anyone who can point me in the right direction to find further information about the vessel and possible crew and passenger information.

Thank you for any help you may be able to give.