Hi Art,
I did a quick check of British National Archives file HW 5/1, and there is at least one reference to the unit, from 17 April 1940. It mentioned an aircraft marked '6N + GK' landing at Oslo at 11:30 on that day, after flying from the unit's base at Lüneberg.
I'd assume that there would be more references to the
Gruppe in ULTRA.
Cheers,
Andrew A.
Air War Publications -
www.airwarpublications.com