What is the most common type of snorkel like ?
The original snorkel parka ( USAF N-3B parka , which is 3/4 length and has a full , attached hood ; the similar N-2B parka is waist - length and has an attached split hood ) was developed in the USA during the early 1950s for military use , mainly for flight crews stationed in extremely cold areas , designed as it was for temperatures down to −60 °F ( ~ −50 °C ) .