so I am wondering if anyone else has researched family in this regiment and has found the ship they sailed on for certain.
Because of security measures surrounding Troopships, It is very difficult to tie down the actual vessel an individual sailed on. Troopships, were never mentioned by name on most official documents but were identified by a code number which changed with every voyage. Regimental War Diaries usually gave this code number.
Likewise there is a lot of conflicting evidence out there. Convoy web is an excellent website but the owner Mike Holdaway would be the first to acknowledge this fact and accordingly doe's not guarantee that his site is 100% accurate.This linked to the fact that many large troopships sailed independently, not in convoy.
Convoy Web says that AQUITANIA sailed from Wellington as an independent on the 15th of Sept 1941. My records and CW says that JOHAN VAN OLDENBARNEVELT also independently, sailed from Wellington on 8/Sept/1941. So on the face of it if your relative sailed on the 15th it must have been on AQUITANIA.
You can download the movement cards of JOHAN VAN OLDENBARNEVELT
http://discovery.nationalarchives.gov.uk/details/r/D8658729And AQUITANIA
http://discovery.nationalarchives.gov.uk/details/r/D8660924Again these records can contain errors, and cannot be guaranteed.
You could also get hold of the vessels Logbooks but in my experience they will not contain details of ports and troop contingents carried.
Unless you have a personal diary or similar giving the name and date of the ship he sailed on I Think the best you can say at this time, given the evidence to hand. Is that in all probability the ship was AQUITANIA.
Attachment taken from the British National Archives. MT40/147