The tanks were ferry only, and only 'YD had them. Why this came about, I can't remember. The capacity was 330 imp gal each - they were gravity filled - and they increased the range by around 600 n.m. This allowed us to make giant strides for a Dart Herald: Kuala Lumpur - Bangkok - Calcutta - Karachi - Bahrain - Larnaca - Belgrade. Then one of the ferry tank pumps failed, so we became a normal version, requiring a stop in Nurnberg, then home to Southend.
Gravity fuelling the ferry tanks at Bahrain 15 October 1977. What our engineer Bernie Riley is doing crawling around up there goodness knows. Perhaps after the python on his head at Sempang he felt it was safer on top!