The military’s three largest drones, made by Northrop Grumman Corp. and General Atomics Aeronautical Systems Inc., have the highest accident rates of any aircraft in the Air Force fleet, Bloomberg News reports.

Northrop’s Global Hawk and General Atomics’ Predator and Reaper unmanned aerial vehicles have had a combined 9.31 accidents for every 100,000 flight-hours, according to data compiled by Bloomberg. The June 11 crash of a drone on Maryland’s Eastern Shore illustrated the vehicles’ propensity for mishaps, the story noted.

The Air Force, in a 15-year period through Sept. 30, recorded 129 accidents involving the medium- and high-altitude drones, the MQ-1 Predator, MQ-9 Reaper and RQ-4 Global Hawk, Bloomberg said.