Yellowtail: The death toll was pretty high for the amount of personnel on the Island, but the support they needed was astronomical. Navy ships shelling the Islands for days before troops landed. Then the conditions were unbelievable for the Army Brass. The Army found out about Muskeg, and frozen terrain. Most Army equipment could not traverse the landscape, or was totally useless in that environment. Resupply with the right equipment was costly and hard. All the equipment the troops had with them was not suited for the arctic. They had been outfitted for fighting in the South Pacific. The mission was so top secret that the army was afraid to resupply them with arctic gear, afraid the Japanese would find out. Plus the Top Army Brass did not understand the conditions they were sending the troops into. A lot of the fighting was done hand to hand, when the Japanese made Banzai Charges.
All things considered the Battle For Attu and Kiska was classified as the second costliest battle of the Pacific Theater. I got that from the reference material I used for my NCO Academy paper. It came from the book "The Forgotten War"