The Mercedes D.III was initially introduced in 1914, at 160 hp. 1914.

It was not in used in this configuration anymore, already in 1916. The designations D.IIIa, au and avu are no official designations, but invented after the war to distinguish them. Every Mercedes 6-cyl engine of that type was called D.III, until 1918, even the D.IIIavu.

Already the Albatros planes from the D.III on in early 1917 received what we call D.IIIa engines developing 175 hp, and the late D.IIIa 185 hp - we do not even differ those; and all earlier ones were changed in the field, with a so-called "Umrüstsatz". Every engine was dismantled and rebuilt after roughly 28 hours of flight, to be updated with the latest field modification "Umrüstsatz", sent to the front.
The upper and lower castings of the engines did not differ, but could be equipped with other cylinder heads, pistons, and crankshafts, or the later oil sumps. The casted numbers and codes of the stripped engines of 1918 still had the D.III code.

It makes no sense to assume that a plane being delivered at the end of july 1917 (CL.II) and in bigger numbers not before november, 1917, would not have received a developed D.III engine.

The Albatros D.Vs already had Mercedes D.IIIa and au engines with 185 to 200 hp - late ones the "au", in various stages.
If you say we have no evidence that e.g. the non-F Fokker D.VII flew with a 1914 160 hp engine in 1918, along with a late 1917 Halberstadt CL.II, you certainly may believe that. I don't.

Cheers,
Catfish

Absolutely have to agree with Catfish, that is just applying common sense!

D.III"a" and "au" engines fitted in the Halberstadt CL.II, link to Viks' reply at the RoF Forum:

http://riseofflight.com/forum/download/file.php?id=29867&mode=view

Although even in this otherwise excellent book there are some small errors, regarding who built the Halberstadts and the performance of the "a" and "au" engines at higher altitude
1. imho it was not BFW for Bayerische Flugzeugwerke, but HFW for Halberstaedter Flugzeugwerke. The "Frakturschrift" "B" often misquoted, is a "H".
2. Link to restoration of a usual Mercedes 200 hp engine, it is just a normal Mercedes D.III from a later series, presumably spring 1918: http://thevintageaviator.co.nz/projects/mercedes-engine/mercedes-engine-restoration

Cheers,
Catfish

Yeah, saw that.

Did someone say the aü engine in the CL.II occurred just in the dev team's imagination?

The interwebs is such a great place for unfairly slagging developers when you're a self-appointed supremo experto HotShot...

"Did someone say the aü engine in the CL.II occurred just in the dev team's imagination?"

I believe the initials are HT.

But to his credit he has maintained an "open-door" to the idea that some sort of documentation that he hadn't seen yet was possible. True, my own arguments carried much in the way of implication and deduction ( which he argued really shouldn't be enough, and I agree ), but Viks posting that page from "Schlacht-Flieger!" sealed the deal...AND locked the discussion.

I do hope you are satisfied, mon Colonel?

If not, then we shall have to pester Dan-San Abbot and Dave Watts over at The Aerodrome with requests for the actual records that "Schlacht-Flieger!" was based on.

I don't give any credit to someone openly accusing the devs to be "liars" without any evidence.
Even without Viks giving the answer with the documentation, there's a big difference between sugesting the dev might be wrong and namecalling them "liars", which is insulting.

The text cited above is from Dan San Abbot, but his contention that the Cl.II had the au engine is what was questioned in the first place. Simply quoting text from one of his books to justify his comments at the aerodrome doesn't address the fundamental issue. It still is not clear that the horizontal air pump was unique to the au.

On the other hand, I think the au engine is getting too much attention. The regular 180hp engine variant is disappointing. Wasn't there any German data to use for it?

BTW Dan passed away last year

If memory serves, he actually called them "liars" and "unethical"; though perhaps I took his harsh words out of context.

At any rate, I think an apology for his impudent words is warranted.