[Milsurplus] unid 80VACvoltage regulator

[Ralph]

I found a coule of small items , similar to dynamotors about 4" long by 
3" in diameter. Marked A Crown M, persumably U.K. Air Ministry. The 
nomenclature states "Ref. No. 5U/1304 Regulator Voltage 80Volts AC" 
"Patent no. 514482 532741"

Can anyone identify what this unit controlled ? One end bell reveals a 
toroidal transformer with 4 leads and the other end a curious 
combination of clutch like assembly. Not sure what principle of 
regulation it uses , perhaps saturable reactor. Its a mystery to me. Can 
supply a photo to the curious. Obviously a piece of airborne equipment.

Thanks

Ralph, VE3BBM