Army Lt. Col. William Joseph O'Brien spent almost his entire adult life in the service of the military. He eventually made the ultimate sacrifice for the nation during World War II, but not before his leadership and actions during the Battle of Saipan earned him the Medal of Honor.
O'Brien was born Sept. 25, 1899, in Troy, New York, to parents Timothy and Charlotte O'Brien. He had two siblings, a brother named Frank and a sister named Evelyn.
According to a 1945 newspaper article from The Troy Record, O'Brien attended Troy Business College after high school, but his education was disrupted by World War I. In 1917, when O'Brien turned 18, he enlisted in the New York State Guard, which replaced the members of the New York National Guard who were drafted into active-duty service.
The Troy Record said O'Brien continued to serve until 1922, when he went back to business college and then worked for a variety of business firms. But his military training must have been calling him, because he eventually enlisted in the New York National Guard, which had returned to its regular duties since the end of World War I.
From there, he made a career out of it. O'Brien got his commission as an officer in 1926 and was promoted to captain by 1939. At some point, he married his wife, Mary, and had a son, William Jr.
In October 1940, as the prospects of entering World War II loomed, the New York National Guard mobilized for active duty with the Army's 27th Infantry Division. O'Brien continued to rise in the ranks, becoming a major in 1942 and then a lieutenant colonel by April 1943, when he was assigned to command the division's 1st Battalion, 105th Infantry Regiment. Eventually, they were sent to fight in the Pacific Theater.
Most of O'Brien's recorded heroics happened during the Battle of Saipan, which started when U.S. Marines landed on Saipan, an island in the Mariana Islands chain, on June 15, 1944. The 27th Infantry Division landed a day later and took the island's airfield within the first 24 hours. From there, the fighting was fierce.
On June 21, when assault elements of one of O'Brien's platoons were held up by intense enemy fire, the commander ordered three tanks to move forward to knock out the enemy's strongpoint. However, because of the enemy's heavy fire, the tanks' turrets were closed. That caused them to lose direction, and instead of firing toward the enemy, they started firing on friendly troops.
With no regard for his own safety, O'Brien ran into full view of the enemy to the tank in the lead. Using his pistol, he pounded on the tank to get the crew's attention. When he finally did, he mounted the tank — still under fire — and directed its assault until the enemy position had been wiped out.
About a week later, on June 28, O'Brien planned a maneuver to capture a bitterly defended ridge. During the action, he personally crossed 1,200 yards of sniper-infested underbrush by himself to get to a point where one of his platoon's was being held up by the enemy. As he ordered four men to stay behind to contain the enemy, he and four others moved into a narrow ravine behind the enemy's strongpoint. They managed to kill or drive off all the Japanese soldiers manning it, and they captured five machine guns and one 77 mm fieldpiece. O'Brien then organized and directed two platoons overnight as they defended against repeated counterattacks, all while managing to hold their ground.
After a few weeks of fighting, the Americans had whittled down the Japanese ranks to the point where they had no reinforcements or place to retreat. So, in the early morning on July 7, 1944, the Japanese commander ordered a final suicide banzai charge — a mass attack made in desperation to avoid surrender and dishonor.
O'Brien's battalion and another battalion got hit by the massive charge, which was estimated to be between 3,000 and 5,000 men. It led to bloody hand-to-hand fighting that overran the battalions' forward positions due to the sheer size of the force.
As people fell and ammunition ran low, O'Brien refused to leave the front lines. He walked among the men there, firing at the enemy with pistols in both hands. His bravery encouraged the other men and kept them in the fight.
Eventually, O'Brien was seriously wounded, but he still refused to be evacuated. When his pistols ran out of ammo, he mounted a jeep with a .50-caliber machine gun and began firing it.
Soldiers last saw O'Brien alive as he was firing at the hordes of Japanese that eventually enveloped his position. Sometime later, his body was found surrounded by the enemies he had killed.
Two days later, the Battle of Saipan ended, having wiped out nearly the entire Japanese garrison. The Allies' successful defeat isolated the few enemy soldiers who remained, and they had no hope for resupply or reinforcement. The battle marked the end of Japanese resistance in Saipan and finally put the Japanese mainland within range of Allied long-range B-29 bombers.
However, the battle still left its mark on the Americans who fought there. According to the New York National Guard, the 1st and 2nd Battalions of the 105th infantry Regiment and the front line of the 27th Infantry Division lost about 650 men to injuries or death. In total, including the Marine forces, the U.S. lost about 3,000 fighters, while Japan lost about 29,000.
O'Brien was posthumously nominated for the Medal of Honor. His widow, Mary, received it on May 27, 1945, from Robert P. Patterson, the undersecretary of war, during a ceremony at Rensselaer Polytechnic Institute in Troy. The Troy Record said that so many people showed up for the ceremony that they had to move it outside, even though it was raining.
Two other members of the 27th Infantry Division received the Medal of Honor for their actions that day: Pvt. Thomas A. Baker, who was under O'Brien's command, and Capt. Ben L. Salomon, a dentist for the 105th's 2nd Battalion.
O'Brien's body was eventually returned to the U.S. and buried in St. Peter's Cemetery in his hometown.
The state of New York has not forgotten him. The officers' quarters at Camp Smith, a New York Army National Guard training site, is named in his honor. In 2014, buildings at Fort Drum, where Guard units train yearly, were named for O'Brien and Baker: the O'Brien Readiness Training Center and the Baker Weapons Training Facility.
This article is part of a weekly series called "Medal of Honor Monday," in which we highlight one of the more than 3,500 Medal of Honor recipients who have earned the U.S. military's highest medal for valor.