"For Iran, the status quo is unsustainable and there is a tacit understanding among all parties involved that Iran has to keep the pressure up," Justin Bronk, a research fellow at the Royal United Services Institute, a London-based defense policy think tank, told DW. "But without crossing any American red lines — specifically, the deaths of American citizens — that would force the US into a military response against Iran, something they do not want to do." Bronk, an expert in air defense, said the more basic category of weaponized drones known as "loitering munitions" are perfect for this. They are comparatively inexpensive and expendable, and can carry around 30 kilograms (65 pounds) of explosives — enough to do some damage and possibly kill, but limited in their potential destructive capacity. "It's all carefully calibrated," he said.