According to the Wall Street Journal, Ukraine’s large-scale drone assault on multiple Russian airbases today—dubbed Operation Spiderweb—was the result of more than 18 months of preparation by the Ukrainian Security Service (SBU). The attack reportedly destroyed over 40 long-range strategic bombers and other military aircraft.

Ukrainian intelligence officials revealed that the SBU covertly smuggled dozens of small quadcopter drones into Russia, followed by wooden containers designed to conceal the drones until the operation was ready. When the time came to strike, the containers were loaded onto trucks and transported near each targeted airbase. Once in position, the lids were remotely opened, releasing swarms of drones to seek out their targets—primarily Tu-95MS and Tu-22M3 long-range strategic bombers belonging to the Russian Air Force.