When I went through ITS we were given money to buy our own SD hats. The Bates were the best as they had floppier crowns that with the help of a damp towel enabled one to arrange it so that it hung over the side and back.
For more operational than the stiff Moss Bros etc..
In the seventies I reprimanded the Bates rep. because his offerings did not resemble my old one and he told me that they had had a three line whip from the Airbox to standardise them with the rest.