Outpost Harry was a remote Korean War outpost located on a tiny hilltop in what was commonly referred to as the "Iron Triangle" on the Korean Peninsula. This was an area approximately 60 miles (100 km) northeast of Seoul and was the most direct route to the South Korean capital.

Most of the fighting occurred at night, under heavy mortar fire, while the daylight hours were usually spent by the UN forces evacuating the dead and wounded, replacing the defending company, sending up resupplies and repairing the fortified positions. The daylight hours were punctuated with artillery, mortar and sniper fire, making repairs and reinforcement a more dangerous task. During the 4 to 5 days prior to the initial attack on the outpost, PVA artillery and mortar fire increased from an average of 275 to 670 per day during daylight hours.

The soldiers of the Greek Expeditionary Force, Sparta Battalion adapted its name and called it Outpost "Haros", the modern Greek equivalent to Charon, Greek mythology's ferryman to the underworld of Hades.

Outpost Harry's elevation was around 1,280 feet (390 m) and positioned some 320 yards (290 m) south of a larger landmass occupied by the PVA called "Star Hill" and some 425 yards (389 m) northeast of UN positions. A service road that wound from the Main Line of Resistance (MLR) along an intermittent stream led to the rear of the outpost where a medical aid station and a supply point were located. Harry was an outpost east of the Chorwon Valley with sister outposts to the west called Tom and Dick. Outpost Dick was about 100 yards (91 m) in front of the MLR, and Tom was about 250–300 yards (230–270 m) in front and below the MLR. The latter was the floor of the valley. Harry, which was over 400 yards (370 m) from the MLR, was also higher than the MLR, making supply much more difficult. The route to the outpost was under constant PVA observation and fire, and its height made it harder to pack supplies up the hill. Unlike Tom and Dick, which could get supporting fire from the MLR, Harry got less close supporting fire from the MLR because company 60mm mortars and the heavy machine guns did not have enough range. Harry relied more on artillery and heavy mortar companies.

The outpost was a strategic position desired by the PVA. Its defense and preservation was viewed as critical because it blocked PVA observation down the Kumwha Valley and shielded that portion of the MLR from direct fire. If the UN forces lost the outpost, the US Eighth Army would have had to withdraw approximately 6 miles (10 km) to the next defensible line.

The position contained a communication trench line which ran from the supply point forward some 400 yards (370 m) to the top. At that point, the trench line joined another trench that made a complete circle around the outpost with an additional finger that ran along the east ridge about 100 yards (91 m). The trench line was deep enough to walk around the perimeter unseen by the PVA. It was fortified with reinforced fighting bunkers, a command post and a forward observation bunker. It could accommodate approximately 150 infantrymen.

During the period of 1–8 June 1953, aerial reconnaissance indicated that the PVA were building for a major offensive. The units identified were the PVA 22nd & 221st Regiments of the 74th Division.

Early on 10 June, K Company, 15th Infantry Regiment, commanded by Captain Martin A. Markley, had been briefed on an imminent attack, and he in turn briefed his men. Ammunition and communications were checked, as were final protective fires.