Hi James,
We went through a lengthy thread on this exact subject back in March, you may want to see if you can reference it.
I have a lot of information from Mercedes and Fokker documenting the early D.VIIs. The offical monthly front line inventories list 19 D.VIIs for April. It turns out 24 D.VIIs were accepted in February and March.
For the "student" I will list them.
227/18
228/18
229/18
230/18 This aircraft was finished by Albatros. 232/18
233/18 At Kest 3 on July 11th, 1918
234/18 Friedrichs crashed into 2 very ealry D.VIIs
235/18
236/18
237/18
238/18
239/18
240/18
242/18
243/18
244/18 Flown by Heldmann, (photos with
LvR)
245/18
247/18 Photo taken of at Jasta 14
248/18
249/18 At Jasta 10
250/18
252/18 Flown by Lowenhardt
253/18
254/18
256/18
So there was certainly some D.VIIs available, it would simply be a matter of if they could have reached MvR before April 21st. Some believe these 23, (1 D.VII would have been type tested to destruction by Idflieg), D.VIIs were still at Armee Flug Parks, or in storage, or in transit from the Flug Parks to the Jastas before April 21st.
Of possible interest, Fokker Dr.Is accepted in September were held at Fokker in Schwerin, (normally the Flug Park would have held them, or they would have been put in storage, but it was known they would go to JG1, so Fokker held them), until more Dr.Is were accepted in early October, and then 17 were shipped out on October 10th and 13th, (one was shipped before, possibly for evaluation on October 4th), so the aircraft type could outfit the entire Jasta, (although this number is still short for a full compliment of 21 aircraft for a Jasta). Another 5 Dr.Is were shipped on October 29th.
If we use this time line of Dr.I aircraft accepted in September and early October, and the aircraft being at the front by around the 20th of October, you can see with the 24 D.VIIs accepted in March, they appear to have had just enough time to make it, or not, to MvR by the 21st of April.
Interestingly enough, if we use the Frontbestand, (front line strengths), for the Dr.I, we see they list 17 for October, so they obviously included the 17 shipped by Fokker on October 10th and 13th, but not the additional 5 shipped on October 29th. Again using this line of thinking, for there to be 19 Fokker D.VIIs listed in the Frontbestand for April, infers they would most likely would have been shipped mid-April and gotten to MvR, or not.
But this is all conjecture and speculation. Until a photo of a D.VII in the field is found with Richthofen in the photo, the side of "no production D.VII was ever flown by Richthofen", will hold the field.
Others believe that MvR was awaiting a BMW powered D.VII instead of the Mercedes powered D.VII, (I believe this unlikely). The very first BMW powered D.VII was 231/18, and it was accepted on April 25th, about month or more after the first D.VIIs were accepted. The next BMW powered D.VII wasn't accepted until a week later on May 3rd.
Best,
Dave Watts