Simons was commissioned a second lieutenant in the Field Artillery Branch in 1941, and was initially assigned to the 98th Field Artillery Battalion, a part of one of the Army's pack mule units. In his first assignment as a platoon leader, he as the new lieutenant was so quiet and reserved (he later said he wanted to learn from the sergeants that seemed to know their business well) that one of his sergeants came to believe that Simons was a mute. The unit was dispatched to Australia, but immediately diverted to New Guinea in the early stages of World War II, and Simons thrived in the harsh jungle environment. He was soon promoted to the rank of Captain and served as a Battery Commander in the battalion from 1942 to 1943. The mules did not prove suitable in the jungle, and the unit was dissolved in 1943. Simons took his battery to the newly forming Ranger Battalion that would come out of the dissolution of his old unit. He soon became the commander of "B" (Baker) Company and later the battalion Executive Officer (XO) of the 6th Ranger Battalion under Lieutenant Colonel Henry Mucci. Simons participated in several hazardous landings with the Rangers in the Pacific. He led a team of engineers and Navy personnel tasked to de-mine the Leyte channel before the invasion of the island began in earnest. On Luzon in the Philippines, he participated in the Raid at Cabanatuan that rescued approximately 500 POWs who were mostly survivors of the Bataan Death March. For his actions in the raid he was awarded the Silver Star. He quickly rose to the rank of Major and continued to prove his worth as a combat leader. At the conclusion of World War II, Major Simons left the active Army for five years.