Ukraine has conducted a series of audacious attacks deep inside Russia against military and economic targets, including at least two drones striking a training facility on Tuesday. Ukraine has used drones to attack Russia before, even striking the Kremlin itself, but Ukraine has never used so many drones in such a short space of time and has never before reached this deep into Russian territory. For over a month, Ukraine’s one-way attack (OWA) drone program has targeted Russia’s production facilities, oil infrastructure, and some of the airbases that facilitate Russia’s missile strikes.

OWA drones like the ones Ukraine uses force defenders to ask hard questions. The first is how do you preserve an expensive and limited stock of air defense missiles? The (relatively) low cost of the drones means that intercepting every single one at a cost comparable to the drone is often difficult. On the other hand, failing to intercept them can be even more costly.