On posting to S&R training in the mid 60s, I was told to go to one of the war surplus shops in Soho and buy an ex Army tank crew throat mic (7/6 -- seven shillings and sixpence). This was handed to the s'quippers to change the connector to aircraft type. Our generous masters eventually organised the replacement with the button types. Clear annunciation was the order of the day but, even so, the quality was akin to mumbling with a mouthful of beans!. I assume, (memory fails!) that for the short period in the 50s when I was on Sycamore S&R, we used normal oxy mask mics.