I was looking at a "blueprint" (sketch) on wikipedia and it showed that the big "box" between the pilot and rear gunner was basically a bomb bay. I assumed this was the fuel tank. I'm thinking the version we have is the version where the fuel tank was moved to the fuselage to get it away from the engines. Can anybody clarify?? My guess is that in earlier models this was a bomb bay but in later models this was the fuel tank and all bombs were carried externally....but just a guess.
Not sure where that image comes from, but I would guess its an 'artists impression' of the Gotha from early on before actual examples were captured.
I.e. a image for journals and newspapers about what the new blitz bomber threat might look like.
They appear to think the main bombload was carried internally like in the 0/400. Presumably on the grounds that if the RFC did that then the Germans probably did too. Or that any big area like that must be used for something - so bombs were the obvious answer.
Whilst the GIV did carry a couple of racks in the mid section, the main load was carried externally underneath. On the GIV the fuel tanks were under the engines - the nacelles going right down to the wing. On the GV in ROF however the nacelles are on struts above the wings so the fuel will presumably have been moved to the middle box (will check up on this).
The GV also lacks the internal bomb racks of the GIV - again indicative of the space being used for fuel not bombs.
Also they are confused as to the layout of the rear tunnel.
Early on there was an awareness of the tunnel amongst the RFC, but no firm knowledge at first. One of the RFC pilots records a Gotha being downed at night. They wanted to check it in daylight to see if there really was a tunnel. But some idiot dropped a cigartte on the wreck and ignited the spilled petrol and burnt it out. They were not happy at the chance to examine it being lost. So at that point they had some idea about such features, but no firm knowledge.
The gangway is also on the wrong side - they must have been aware of it, but once again not had the firm details.
So the sketch may be from that 'what we we think it looked like' period.
(See the Wingnut Gotha instructions for a Gotha GIV layout includingthe intenal bomb racks -
http://www.wingnutwings.com/ww/product?productid=3006 )