I saw this posted on Brass Goggles and thought others here would find it interesting.
According to the source:
Leather flying helmet with 10A/12401 headphones, an oxygen mask and a 10A/12570 microphone. At the outbreak of WWII (1939-1945), flying helmets had changed little since WWI (1914-1918), except that the fittings for goggles and oxygen masks were provided. The flow of oxygen to the detachable mask was controlled by a manually set regulator. Gosport tubes or radio microphones were used for communication between the crew. Made for the Air Ministry.