Water cooled steel vanes is correct.
From 'German Secret Weapons: Blueprint for Mars', Brian Ford, 1969:-
"Right from the start, when tests began, there were problems. In spite of an initial acceleration of 2g or more, the craft left the upright launcher at a speed of only 30-40mph - far to slow to alolow the wing flaps to exert any aerodynamic effect.Clearly (as in the V-2),some exhaust deflectors in the jet stream were needed. But how could they be included and still make the proposition economically sound? The answer was simple, steel vanes were included, each one hollow and filled with cooling water. There was no circulating pump or protective mechanism, indeed, none was necessary. Admittedly, after some seconds they would begin to heat up, then as the water boiled away, they would eventually melt away in the rocket gases, but by then enough altitude had been reached for conventional controls to become effective.
So an entirely new, and very viable notion was introduced - disposable, temporary control surfaces"
also from 'Warplanes of the Third Reich', page 67:- "...and small water cooled control vanes were introduced in the rocket engine orifice, these having a life of approximately 30 seconds by which time enough speed had been attained to render the normal control surfaces fully effective..."
cheers,
Robin.