Which preposition to use with undersecretary

at Occurrences 1%

Her husband had been named undersecretary at the Ministry of Public Works in the new cabinet, and she was very pleased.

of Occurrences 1%

For a scant instant Mr. Grimm's eyes rested on a young woman who sat a dozen feet away, talking, in playful animation, with an undersecretary of the British embassya young woman severely gowned in some glistening stuff which fell away sheerly from her splendid bare shoulders.

to Occurrences 1%

Lord Hatherley's influence obtained for my brother the post of undersecretary to the Society of Arts, and also some work from the Patent Office, and my mother went to live with him.

Which preposition to use with  undersecretary