The operation a year and a half in the making involved secret cooperation between agents, drone operators and technicians in the intelligence service.

From: Washington Post By David L. Stern
KYIV — For one year, six months and nine days, Ukraine’s intelligence service carefully plotted, designed and built special drones, concealed in prefabricated mobile homes that were then transported across borders to strike a surprising blow thousands of miles away against Russia’s strategic bomber fleet.
Intelligence chief Vasyl Maliuk revealed to journalists new details of “Operation Spiderweb” in a two-hour conversation Sunday about the plan to attack Russia’s air bases that crippled several long-range bombers and rewrote the rules for drone warfare.
Ukrainian security officials have said the June 1 attack destroyed 12 Russian aircraft, including the Tu-95long-range bombers that the Kremlin uses to target Ukrainian cities with missiles, and hit 41 aircraft in total.