This 5-stamp series of forgeries of the German East Africa yacht issues was discovered in the years after WWI, but the stamps’ exact provenance is still a mystery.
The stamps are not believed to have been intended as true forgeries, as they are so different in design quality and size that they could not possibly have fooled users. Most theories place there origin within the British propaganda executive during the period from 1916-1918, though there are competing theories that they are of Italian origin post-WWI, or produced as provisional issues by German forces in DOA during 1917.
Cinderella expert Harry F. Rooke referred to the stamps as the “Karissimbi provisionals”, though the reason for giving them this name is unknown. Karissimbi is a volcano that was in the western part of German East Africa.
They are known to exist unoverprinted, overprinted “G.E.A. BRITISH OCCUPATION” with new value, and overprinted with forged cancels. Imperforate copies are also known.
The name may have originated with a Paris dealer who noted, in 1919, he had received from "Karissimbi" a registered cover with a set of these that had gone through military censorship. Other covers with the same postmarks have come to light since then. I believe they may have been dated Dec 1918 or 1 month after the armistice.
The main theory seems to be that they are British in anticipation of the eventual German defeat. If so why are many not overprinted and would they bother with the situation in East Africa when there were other worries closer to home.
The name "Karissimbi Provisionals" seems to indicate a possible local printing perhaps due to some shortage?
Why not just have a look to the Michel-Catalogue ?
Quote: Schiffstype zu 2 1/2,4,7 1/2,15 und 30 H. in größerem,besonders unverhältnismäßig höherem Format mit Aufdruck G.E.A. BRITISH OCCUPATION,ist eine von feindlicher Seite angefertigte,auch mit falschen Feldpoststempeln vorkommende Schwindelausgabe.
translated it means: Ship-type issue 2 1/2....H. in a larger,non-propotional higher size,overprinted..... is a from enemy-side produced,also existing with faked fieldpost-cancels,fraudulent issue.