Well, here's the one we got...
https://eos.org/features/the-geomagnetic-blitz-of-september-1941
Upside, thermionic valve electronics are a lot more tolerant of such mayhem than our nm-scaled, low-voltage micro stuff. And, remember, systems were far less 'wired'. You'd probably have a lot of plug-type and 'Strowger' electro-mechanical phone exchanges blowing their 'lightning' fuses, staying off until things calmed.
Long US power lines from eg Niagara & Hoover Dam may go down hard. Ditto, the Ruhr ?? IIRC, Russia tended to have power stations more local...
Um, ships' systems endure electrical storms, St Elmo's Fire, even lightning strikes, so it would be a case of replacing fuses and resetting breakers. War at sea continues.
Landlines would suffer, but teleprinters & Enigma-style code machines will be safely isolated when their telephone exchanges shut down. 'C&C' and Land war continue.
Aircraft didn't run on micro-electronics, fly-by-wire etc, so the 'War in the Air' continues.
One possible 'gotcha' is UK's Radar network which, running on much longer wavelength than German equivalent, needed much bigger antennae and is more vulnerable to outages. Still, neither side will have time for more than local, tactical reaction before the storm subsides...
Added...
Found this, too.
http://www.solarstorms.org/SRefStorms.html