Actually you needed
a fairly deep coat pocket, but Horace Dall travelled the world with a 150 mm
reflector of his own design in his pocket. In the days before metal
detectors, he was not once stopped by customs!
As you can see from the pictures below, taken in 1978, the secondary mirror was held on an arm that folded flat across the main mirror, which was also hinged to fold down. The eyepiece was in a short tube that was carefully baffled to exclude a view of the sky beyond the secondary, so it could be used by day. The Dall-Kirkham design gives excellent erect images with a long focal length.