Kerryn Offord wrote in

Didn't the original research for stealth come out of Russia (or at
least was done by Russian mathematicians...

In a-round-about way,

According to Ben Rich's book, the original formulas were from a scottish
physicist James Maxwell,developed a century ago, later refined by a german
electromagnetics expert Arnold Sommerfeld, then put in a paper by a
russian radio engineer scientist named Pyotr Ufimtsev ,paper was called
"Method of edge waves in the physical theory of diffraction"
that paper was ignored for 9 years until translated and discovered
by a Skunk Works mathemation named Denys Overholser.
once he understood the theory, stealth came into being.

REF:
Skunk Works" by Ben Rich & Leo Janos.
page 19

IMHO:
One Hellofa read, well worth having on your book shelf.