Allied forces suffered over 500 casualties in total during the operation from Japanese landmines and booby traps, friendly fire incidents, and vehicle accidents.

[citation needed] After the heavy casualties suffered at Attu Island, Japanese planners were expecting another costly operation.

Aerial photograph analysts noticed that routine activities appeared to greatly diminish, and almost no movement could be detected in the harbor.

Progress was also hampered by mines, timed bombs, accidental ammunition detonations, vehicle accidents and booby traps that caused further casualties.

[2] A stray Japanese sea mine caused the USS Abner Read (DD-526) to lose a large chunk of its stern.