During the nineties the Swiss built a total of four Bison batteries, each consisting of two casemates with both two 155 mm guns. However to test the concept they built a prototype near Halsegg. It also consisted of two casemates, but they were armed with 105 mm guns. Each of the casemates differs on several small points. However what they have in common is a rather vulnerable entrance which is in fact a shaft protected only by a wooden shed.