As Army head of operations he unsuccessfully advocated a policy of nuclear armament as a deterrent against the Warsaw Pact in the 1960s.
Switzerland eventually ratified the Nuclear Non-Proliferation Treaty.
As Chief of the General Staff, holding the rank of Korpskommandant (NATO: OF-8), Senn was Switzerland's most senior military officer from 1977 to 1980.
After his retirement, he authored two standard works about Swiss defence efforts during World War II.