Complex sentence: Having been adopted as a protégé by Pavel Sudoplatov, Fisher took part in Operation Scherhorn (Операция Березино) in August 1944, described as "the most successful radio deception game of the war".
Split into simpler sentences: Having been adopted as a protégé by Pavel Sudoplatov, Fisher took part in Operation Scherhorn (Операция Березино) in August 1944. Sudoplatov later described this operation as "the most successful radio deception game of the war".