Doing a bit of research into G-AODA there are some discrepancies with a couple of the previous comments.
Firstly the vessel "Linguist" appears to have been scrapped in 1969 and I can find no trace of a replacement with that name since,so the 1975 memory appears suspect?
Secondly the photo caption suggesting DA was the first conversion is definitely incorrect.It was actually the 14th ,going through the process between Feb- July 1965.
Finally the markings Heli Taxi are intriguing. Were these carried for its time in Iran between 65 and 68?
Christmas Quiz?!