But the study also finds that strikes carried out by unmanned aerial vehicles cause fewer civilian casualties than other kinds of combat and that those deaths don't appear to be linked to further violence against U.S. forces and allies.
Capt. Paul Carey of the Maryland Natural Resources police shows a side-scan sonar being used in a search on the Chesapeake Bay in 2006. In recent years, the cost of such equipment has come down, allowing more local law enforcement departments to purchase it.
Credit Chris Gardener / AP
(This post was updated at 11 a.m. on Sept. 27.)
There's been a number of stories lately about astonishing discoveries by law enforcement using side-scan sonar.