I'm wondering if the AEO occupied what had once been the second nav's position?
https://www.rafmuseum.org.uk/documen...over-XS639.pdf
To No. 115 Squadron, RAF Brize Norton, Oxon operating all the E.3/E3A aircraft as part of No. 90 Group.
Painted in a high visibility scheme of white and light aircraft grey with signal red cheatline, engines, wingtips and tail unit. Operated transport tasks in addition to calibration duties.
XS639 was one of three E3A ‘hack’ aircraft used by the Squadron in a variety of roles, primarily transport of passengers and freight. Though not fitted with specialist radar equipment, the E3A could be used as a passive radar target.
They were identical to the C.1 though with the addition of an extra crew position alongside the navigator.......