On D-Day in World War II: "At 2:30 a.m. the network was put on 'flash' basis; the NBC four-chime-alert calling all newsmen and commentators to their microphones, key operating personnel to their stations, sounded from the newsroom control room"
The fourth chime and NBC Radio's announcement of D-Day are here: http://www.nbcchimes.info/nbcsounds.php
Edit: it appears the pronunciation in the UK is the same one used in the audio, according to https://en.m.wiktionary.org/wiki/allied.
I'd hazard a guess this means the US pronunciation has evolved over time
Cary Grant and Katharine Hepburn were among the best-known practitioners of this accent. It was very common in movies and newscasts back then.
In the NBC Chimes Museum article, the announcer in the first audio clip under "1944 the fourth chime" is another good example of the Mid-Atlantic accent.
Use Yah Blinkah
Stay Wicked Fah Apaht
[1] which explains why I am also a fan of Mister B, who puts the RP in RaP.