From The Miami News on this day in 1936:
The Queen Mary's Rudder - The largest rudder ever carried by any ship now hangs at the stern of the superliner Queen Mary, ready, like a giant fish tail, to compel the waters to obey its slightest turn. Some idea of the high metal strength of this huge rudder may be gained when it is realized that it must control no less than 80,733 gross tons, the tonnage of the great Cunard White Star sea queen. The rudder, with frame, weighs 270 tons, which is 90 tons heavier than the entire weight of the Pilgrim ship "Mayflower." Interesting features of the Queen Mary's rudder are the two doors which have been fitted into the sides, and the permanent steel ladder running through the "compartment" enclosed by the steel walls of the rudder. Inside there is ample room for several men to walk about. Struts and bars hold all rigidly in place. The great rudder hangs between the lower two of the ship's four big propellers, each of which weighs 35 tons.
Photo of Queen Mary rudder being transported to Glasgow: