Early 20th century (in an earlier sense). From Spandau, the name of the westernmost borough of Berlin, site of the arsenal where guns of this kind were first developed.
Definition of Spandau in US English:
Spandau
noun
Military
A Spandau gun.
Origin
Early 20th century (in an earlier sense). From Spandau, the name of the westernmost borough of Berlin, site of the arsenal where guns of this kind were first developed.