USAAF oxygen masks
All the american oxygen masks were made of rubber and research on oxygen supply systems was already done before the US entered the war. The early oxygen masks covered only the nose part while the mouth was kept free for communication. Later on the mouth was also included in the oxygen mask and a microphone was installed in the oxygen mask body.
Early masks used special hooks sewn on the helmet to attach the mask while the newer masks used press studs to attach the mask.
The US used 2 different types of oxygen mask systems, continuous oxygen flow and later on the oxygen demand system. Those 2 systems needed a completely different oxygen mask design and the continuous flow was only used for the early mask (A-7, A-8 series and A-9, A-10)
Some oxygen masks were covered with chamois to improve comfort but this was a field modification patterened after the RAF masks.
Early oxygen masks
Left: A-9 oxygen mask with a "Juliet" for wearing the mask without flight helmet. The hose is not the original hose which should be grey just like the mask.
Middle: A-10 standard oxygen mask with "Juliet". The A-10 standard was the only oxygen mask which used a central strap across the forehead.
Right: A-10R (revised) oxygen mask. This is more or less an A-10 standard oxygen mask without the central face strap and which can be attached with press studs instead of the hooks.
Later oxygen masks
Left: A-10A oxygen mask.
Middle: A-14 oxygen mask shown with original issue box. Note the microphone is installed on this example.
Right : E-1 heater in place on the A-14 oxygen mask.
Left: Close up of the E-1 heater.
Middle: Original instruction paper and accessoirs for the E-1 heater.
Right: View of the E-1 heater instructoin paper.