The first 2 digits are reference to the case material:
01 (stainless steel) which is pretty obvious here
The last 3 digits are reference to the movement:
505 is cal. ETA - ESA 9164 (tuning fork movement).
Rössler says that this movement was called Zenith Caliber 50.0 under licence from Bulova & Pat.
So I guess we are looking at Zenith XL-tronic's case: