Congratulations !!! That really was a bargain !!
Indeed, these are very often (but not always) Kriegsmarine Gasmasks.... much more difficult to find...
You can check the inside of the mask between the eyes if there is a Eagle stamp with a big M. If that is the case it is a Kriegsmarine Mask
Also check the spare lense compartement on the inside if there is a Eagle with M stamp
Here a pic of a GM30 with mike attached