It is known that Donald G. Haines of RCA applied for a patent for the pentagrid on 28 March 1933 (subsequently granted on 29 March 1939) under US patent number 2,148,266. The pentagrid also featured in a UK patent (GB426802) granted on 10 April 1935. However, the Ferranti company of Great Britain entered the valve business with the first known UK-produced pentagrid, the VHT4, late in 1933 (though it must have been in development, and would certainly have existed as a prototype well before that time).