English: This photo, taken in August, 2010, looks northwesterly and shows three concrete columns that used to serve as the bases for depression position finder (DPF) instruments that were used by the U.S. Coast Artillery to control the fire of their gun batteries. These three columns were part of the fire control system at Fort Warren on Georges Island in Boston Harbor. They are located atop Bastion E in the southwest corner of the fort.

The two nearest columns were enclosed in one fire control building and the one in the background was in a separate building. Originally, a floor existed at a level that would have put the roughly four foot-tall instrument at the user's eye level. The roofs, floors, and walls of these buildings, built in the period 1905-1920, have since collapsed and disappeared.

The barrel-shaped building behind the second column is an old magazine, likely left over from the time when powder for muzzle-loading cannon was stored in this area.