If the mask floods, the diver can continue to breathe while clearing the mask, and it minimises dead space. Many Royal Navy and frogman's rebreathers have this mask arrangement. It makes clear talking difficult, but not impossible. For many years British armed forces divers used the Admiralty Pattern full face mask, with a long rectangular window, largely flat, and bent back 90° at the ends, as in the illustration of a diver with a CDBA rebreather. The lower skirt has a hole that a breathing set mouthpiece is fitted through.