O.Thetford, P.Gray German Aircraft of the First World War (Putnam)
Fokker W 4
This aircraft was a seaplane development of the M 7 which had also been used by the German Navy. Only a few short flights were made during March 1915. Engine was 80 h.p. Oberursel U O rotary.
Форум Breguet's Aircraft Challenge
Quoting from the Nowarra based text of Marine Aircraft of the 14-18 War p.81
"....In the same year Fokker built his last floatplane of the period, the W4. The fuselarge of the M7 was used and, like that aircraft the new floatplane was of sesquiplane configuration, although a larger span necessiatated two bays of strutts. The W3 was a private venture by Fokker. It (the W3) was a hydroplane powered by an aircraft engine, that he (Fokker) used for trips over the lake at Schwerin, more for amusement than to gain experience of handling floatplanes."