Grammatical item as to the use of "what"?

Question

"Several weeks ago, the level of the public discussion here was raised in a rather quiet fashion. In what was an unusual speech to a group of hard-nosed businessmen, the president addressed a meeting of the Association of Banks."

Why does the last sentence shown above not begin with simply "In an unusual speech to ..." instead? What purpose does "In what was" serve in fact?

Answer 1

The "In what" allows the inclusion of "was", firmly placing the event into the past tense.