CH 1942 Z37a Recycling of old materials FDC with address

Switzerland 1942 Recycling of old materials (Durchhalten, Tenir, Resistere),
FDC Stamps of different denominations connected (Z37a), Horizontal stripe of three: German - French - Italian,
neutral registered letter (rarely subscription letter) with address,
cancelled "21.III.42 Bern - Briefannahme", sender Gaudard,  top quality,
Catalog SBK Z37a (254-256), Michel  W Zd. 7 (405-407).