02/28/2011. The WD 13 was almost identical to the WD 12 (an enlarged version of the WD 9), and similar in size and weight, the WD 13 (alike the WD 12) was fitted with a Daimler D III engine. Eighteen WD 13 observer aircraft were produced, while an additional small number of the WD 13a were also produced, with smaller dimensions and a Benz Bz III engine, these were delivered to Turkey between January and April 1918.