Ukrainian President Volodymyr Zelenskyy said on Saturday that Kyiv's troops were fighting in Russia, days after reports emerged that Ukraine was breaking Russian lines in Kursk.ROMAN PILIPEY/AFP via Getty ImagesUkraine launched its attack on Kursk on Tuesday but has said little about its incursion.That contrasts with its failed counteroffensive in 2023, when it even released a teaser video.While remaining largely silent on Kursk, Kyiv says it has taken nearly 400 sq miles of Russian territory in days.As Ukraine pushes further into Russian territory this week, it's becoming increasingly clear that Kyiv was leaning on one key factor of its surprise attack on Kursk: the element of surprise itself.Kyiv claims to have gained control of nearly 400 square miles of Russian territory in just a few days, which is nearly as much Ukrainian territory seized by the Kremlin in 2024 so far.The New York Times' report on the prelude to the bold, cross-border attack gives a glimpse at Ukraine's emphasis on secrecy this time.According to The Times, a research institute affiliated with Ukraine's military had studied successful campaigns in modern history and found that the winning side often said nothing publicly before their attacks.That doctrine seems to have cascaded to troops on the field.A Ukrainian deputy brigade commander, identified by The Times as Lt.