The 'Battle of Lone Tree Hill' was a battle between US and Japanese forces in the Netherlands New Guinea (17 May/2 September 1944).

Part of the Western New Guinea campaign, the battle and the associated attacks on Sawar airfield 10 miles (16 km) to the north and Wakde island just 8 miles (13 km) to the north of Toem took place after the opening phase of the campaign, which saw landings at Hollandia and the Aitape late in April.

Following their loss of Hollandia, to the east, to the US 'Reckless' assault of April 1944, for the Japanese the 26 miles (42 km) of shoreline and surrounding area of Toem-Wakde-Sarmi was an isolated coastal salient. Nevertheless, elements of the 223^rd Regiment and 224^th Regiment of Lieutenant General Hachiro Tagami’s 36^th Division, were concentrated at Lone Tree Hill, overlooking Maffin Bay, and in that location blocked any farther US advance toward Sarmi by the 158^th Regimental Combat Team of Major General Horace H. Fuller’s (from 18 June 1944 Major General Jens A. Doe’s) 41^st Division in Lieutenant General Walter C. Krueger’s US 6^th Army. The Japanese held well-prepared positions, which included fortified caves. Meanwhile, the main body of the 223^rd Regiment had outflanked the US units, and a battalion of the 224^th Regiment, was retreating from Hollandia toward the Toem-Wakde-Sarmi area.

The feature which became known as Lone Tree Hill rises from a coastal plain about 2,000 yards (1830 m) to the west of the main jetty in Maffin Bay. The hill received its name for a single tree on its summit on US maps; the hill is a coral formation covered with dense tropical rain forest and undergrowth. It is about 175 ft (53 m) high, 1,200 yards (1180 m) long on its north/south axis and 1,100 yards (1005 m) wide on its east/west axis. The northern side is characterised by a steep slope, and the eastern slope is fronted by a short, twisting stream which the Americans named Snaky River.

On 14 June, Krueger sent Major General Franklin C. Sibert’s (from August Major General Edwin D. Patrick’s) 6^th Division to relieve the 158^th Regimental Combat Team. After 10 days of hard fighting, the US forces took Lone Tree Hill. The Japanese suffered the loss of more than 1,000 men killed, including some trapped in collapsed caves. The US Army suffered about 700 battle and 500 non-battle casualties. By 1 September, there were still around 2,000 Japanese troops in the area, but they no longer posed a threat to Allied operations. With Lone Tree Hill in US hands, Maffin Bay became a major staging base for the subsequent battles for Biak, Noemfoor, Sansapor, Leyte and Luzon.