The Myth - A frozen chicken launched in a bird strike simulation can penetrate aircraft or train windshields better than a thawed chicken.
Verdict - Busted (later overturned)
Notes - After building a large air gun, the MythBusters fired saboted chickens at a fuselage portion, and later at a metal plate viewed with a high speed camera. Originally, impact time or force transferred was the same for both frozen and thawed chickens, but this test was not conducted using airline-qualified glass rated for a bird strike, which has a thicker consistency than normal pane glass. This verdict was later overturned in the Myths Revisited episode.
The original myth involved the British borrowing the titular gun for testing train windshields, but were shocked and confused at the amount of carnage the gun did. When they asked the Americans what they were doing wrong, they were told to thaw the chickens before firing.