Hi,
I wish I had joined Rootschat before yesterday, I was in the Greenwich Heritage Centre then looking for the same information as you! I might have been able to help! My great grandfather took his family to Constantinople between 1863-1866 and returned sometime before the 1881 census. I have births for two of his children, marriages for four of his elder children, plus several births of their children, whilst they were there. I'm not sure whether Woolwich Arsenal sent him there but that is what the family story says. He was an engineer but of what type I don't know. It has been assumed that he was a marine engineer but now I'm not so sure, he might have worked on railways. Either way, another family story says he was out there teaching the Turks how to use the new munitions Britain was supplying them in their war against the Russians. I've just been informed by a volunteer at the Greenwich Heritage Centre, who is also a member of the West Kent Family History Society, (as am I) of two web sites I found interesting, which you might like to view. "The Building of Istanbul Docks - 1870-1910" and "Old and New Photographs of Istanbul" (by Maggie Blanck). If you are not a member of the WKFHS I would recommend you join, they are very helpful and enthusiastic. Hopefully I will hear from you at some time but in the meantime good hunting.
Victor