The Gueneau ZEUS C was one of the three helmets tested at the end of the 80s, with the aim to identify a lightweight helmet with which to equip the crews of Swiss AF new generation combat aircraft. 

Competitors the Swiss built “Titlis” prototype and the Gentex H/ATS (Toptex 3).

Very positively judged, nevertheless the helmet had a problem; the distance between pilot's face and the inner visor being too small, preventing wearing glasses. Fitted to the helmet an EROS MP-90 oxygen mask.

Interestingly, the evaluation had no winner, none of the three helmets would become the selected one. In fact the “winner”, out of competition, was the HGU-55, implemented without a real evaluation.

Below a scan of the cover of the September 1989 issue of  "Aero Revue" magazine. It features  Pilatus chief test pilot Hans Galli on board a Pilatus PC-9.