First use of the expression "Spandau Ballet"

Am wondering about the known history of this term. I assume that

• Spandau refers to the German MG08.

• The term as a whole refers to the behaviour of massed troops being hit by machine gun fire.

• The term is approximately as old as the phenomenon, i.e. early 20th century colonial wars, or WW1.

But which is the first occurrence? Letter? Memoir?

Currently the earliest attested use I am aware of is the c. 1980 Berlin public restroom decoration from which the noted entertainment ensemble took the name.

For noise reduction purposes I note that alternative explanations of the term include group hangings, Rudolf Hess, and gas chambers. Am sure there are many more, but let us try to focus on the earliest occurrence of the term.

That book (Bolt Action: Armies of Germany) adds nothing new.

A recent article:

In the First World War, the phenomenon of soldiers, bodies freshly wracked by machine gun fire, writhing to their deaths while agonisingly propped up by barbed wire, was given the truly grisly nickname of “the Spandau Ballet”.

(But closer to ballet without the wire.)

I knew of the expression many years before it was appropriated by the now famous pop group. I remember thinking back then that their choice of name was in bad taste, given the original meaning. Both of my grandfathers fought in WWI and it may be that one of them told me the original meaning. It apparently referred to the British soldiers bodies jerking uncontrollably as bullets fired by the German machine guns hit them again and again. The Germans had Spandau machine guns, as has already been noted, and each one sent a lethal hail of bullets into the advancing ranks of soldiers.