What you speculate, Ashley, may well be right, but my understanding (from the Forum posting rules) is that this Forum goes to some trouble to keep genuine historic archive material separate from individual's interpretations.
I am a moderator on another (warships) board where the solution we have adopted depends more on clear labelling than on rigid separation, but the problem is the same: someone will copy your (unlabelled) Frankfurt, post it elsewhere, and another "ghost" is set free to look real.
But the Kriegsmarine was certainly interested in AA ships. You may like to look at
PS Yours is a nice drawing, though, and a realistic concept.