He became a second lieutenant in the Marine Corps in 1942 and graduated from the Reserve Officers' Training School in Quantico. He served with the 1st Marine Division on Guadalcanal, and was commanding officer of Company K at Cape Gloucester, where he received the Silver Star for leading hand-to-hand combat in a fight on Walt's Ridge. He led Company K through most of the fight for Peleliu. Haldane was killed by a Japanese sniper on October 12, 1944, while assessing the area of Hill 140 during the Battle of Peleliu in the Palau Islands, three days before the Marines came off the lines. A Sea Scouts Ship was named in his honor at his old college.