E.R.A. on German U-Boats

[Einbauschrank]

Hello!

My girlfriend is wading through the British secret reports made from eavesdropped conversations between German POW in the Mediterrenean for her Master. The reports were compiled by German immgrants who translated the German ranks into the British equivalent. This is normally easy enough but there are some acronyms that totally esacpe me.

Could anyone enlighten me as to what "E.R.A." refers to? In the files she has it only appears in the U-Bootwaffe. If it is extra regimental asignement: why would you call assignment to a U-Boat "extra regimental" and can the function and rank be narrowed down? Is it an officer or an enlisted rank?

Thank you for all hints!

Patrick