Rank and organization:   Lieutenant Colonel, U.S. Army, 1st Battalion,
105th Infantry, 27th Infantry Division.
Place and date:   At Saipan, Marianas
Islands, 20 June through 7 July 1944.
Entered service at:   Troy, N.Y.
G.O. No.: 35, 9 May 1945.
Citation:   For conspicuous gallantry
and intrepidity at the risk of his life above and beyond the call of duty
at Saipan, Marianas Islands, from 20 June through 7 July 1944. When assault
elements of his platoon were held up by intense enemy fire, Lt. Col. O'Brien
ordered 3 tanks to precede the assault companies in an attempt to knock
out the strongpoint. Due to direct enemy fire the tanks' turrets were closed,
causing the tanks to lose direction and to fire into our own troops. Lt.
Col. O'Brien, with complete disregard for his own safety, dashed into full
view of the enemy and ran to the leader's tank, and pounded on the tank
with his pistol butt to attract 2 of the tank's crew and, mounting the
tank fully exposed to enemy fire, Lt. Col. O'Brien personally directed
the assault until the enemy strongpoint had been liquidated. On 28 June
1944, while his platoon was attempting to take a bitterly defended high
ridge in the vicinity of Donnay, Lt. Col. O'Brien arranged to capture the
ridge by a double envelopment movement of 2 large combat battalions. He
personally took control of the maneuver. Lt. Col. O'Brien crossed 1,200
yards of sniper-infested underbrush alone to arrive at a point where 1
of his platoons was being held up by the enemy. Leaving some men to contain
the enemy he personally led 4 men into a narrow ravine behind, and killed
or drove off all the Japanese manning that strongpoint. In this action
he captured S machineguns and one 77-mm. fieldpiece. Lt. Col. O'Brien then
organized the 2 platoons for night defense and against repeated counterattacks
directed them. Meanwhile he managed to hold ground. On 7 July 1944 his
battalion and another battalion were attacked by an overwhelming enemy
force estimated at between 3,000 and 5,000 Japanese. With bloody hand-to-hand
fighting in progress everywhere, their forward positions were finally overrun
by the sheer weight of the enemy numbers. With many casualties and ammunition
running low, Lt. Col. O'Brien refused to leave the front lines. Striding
up and down the lines, he fired at the enemy with a pistol in each hand
and his presence there bolstered the spirits of the men, encouraged them
in their fight and sustained them in their heroic stand. Even after he
was seriously wounded, Lt. Col. O'Brien refused to be evacuated and after
his pistol ammunition was exhausted, he manned a .50 caliber machinegun,
mounted on a jeep, and continued firing. When last seen alive he was standing
upright firing into the Jap hordes that were then enveloping him. Some
time later his body was found surrounded by enemy he had killed His valor
was consistent with the highest traditions of the service.
This data was extracted from the Committee on Veterans' Affairs, U.S. Senate, Medal of Honor Recipients: 1863-1973 (Washington, D.C.: Government Printing Office, 1973)