Silver voiced porters announce train destinations at sloane square speeding up London underground . In order to assist passengers travelling on the Underground railways , loudspeakers and a microphine has been installed at Sloane square station and porters announced the stations at at which trains call enabling passengers to be sure they are on the right train and speeding up the new departure of the vehicles . Porter Donnovan announcing train destinations at Sloane Square staion , London . 8 February 1932