While the rest of Radio Almanac was a silly and fairly unsuccessful bid by Welles to become a radio comedian (and with the poor scripts the show had it would be hard to succeed,) the Invasion of Europe prompted Welles to offer the one serious broadcast of the entire series (and the adrenaline of the previous day seemed to engender a superior script as well.) The day America rolled the dice, with the certainty of massive loss of life, in a gamble to change the shape of the world was no time for buffoonery.
Welles is barely present in the show (due of course to some deep-seated psychological reason,) and Agnes Moorehead provides her last starring role under Welles' direction (while she was a regular on the Almanac series, the rest of the time she portayed a long-suffering member of The Orson Welles Swoon Club.)
Though the credits don't mention it, that sure sounds like a Bernard Herrmann score to me. Lud Gluskin provided the appropriately brash music for the rest of the series, but the sombre hand of Benny was more suitable here.