What are pea coats which is now spelled as one word peacoats?

A pea coat is a heavy wool winter coat that has buttons with anchors on them. It is worn by members of the United States Navy. It is commonly referred to as a Navy pea coat. : A peacoat is a sailor's heavy woolen double-breasted jacket. : like this one: : http://www.shopyop.com/product_424.html