During World War II Winston Churchill traveled thousands of miles. In the beginning he usually traveled on naval vessels. As the war continued, he used airplanes more and more. He was old, he had a bad heart, he smoked continuously, and drank like a fish.
Remember that this was in the days before cabin pressurization. Obviously, it was safer for him to travel at high altitudes, in order to avoid attacks by German aircraft. What to do .... well they did this:
Designer Graham demonstrates Winston Churchill’s personal pressure chamber, created to enable him to make high-altitude flights safely. In: Life, 10 Feb 1947.
To protect the precious bulk of Winston Churchill in wartime a special one-man pressure chamber was built for the personal plane which carried him many times across the Atlantic and to Casablanca, Moscow and Yalta. Churchill was warned by his doctors that it was dangerous for a man of his age and physical condition to fly above 8,000 feet. The solution was a pressure chamber complete with ash trays, telephone and an air-circulation system good enough to prevent smoke from the ubiquitous cigar from fogging the atmosphere.
source (in German): http://www.crackajack.de/2012/01/24/winston-churchills-pressure-chamber/
He liked to wear a sort of velvet jumpsuit when he flew, too.