The military post owed its name to William Axel Hertz, a British civil servant who led the first expeditions into the far north of Burma in 1888. Hertz spent decades mapping and administering this spectacularly remote territory, producing the 1912 Gazetteer of the Kachin Hills area and serving as the first Deputy Commissioner of the Putao District. The outpost was established in 1914 near the present town of Putao, but it was not given its name until 1925, upon Hertz's retirement from the Indian Civil Service. Before the war, the Burma Frontier Force's Myitkyina Battalion maintained it as a quiet border station. The surrounding landscape of dense jungle, soaring peaks, and monsoon rains made overland access extraordinarily difficult, a geographic reality that would prove both curse and salvation.

When Japan invaded Burma in 1942, Fort Hertz was cut off. Military authorities in India lost all contact for most of that summer. On July 3, Captain J.O.M. Roberts of the 153rd Gurkha Indian Parachute Battalion parachuted into Upper Burma with orders to assess the situation around Myitkyina, then march 150 miles north to the fort. He reached it before anyone expected. When Major Hopkins overflew the site on August 12 and confirmed it was still British-held, the landing strip was unusable. The very next day, Captain G.E.C. Newland parachuted in with engineering supplies. By August 20, the airfield was patched together well enough for aircraft to land, and Lieutenant-Colonel Gamble arrived as the new area commander, followed quickly by a company of the 7/9th Jat Regiment. Among those extracted around this time was Captain Arthur Thompson, who would later become the novelist Francis Clifford, drawing on his wartime experiences in Burma.

The garrison that held Fort Hertz was a patchwork force: battalions of the British Indian Army and the Northern Kachin Levies, supported by Kachin irregulars who knew the terrain intimately. Together they defended the route north from Japanese-held Burma through a series of minor but persistent engagements in 1942 and 1943. Large-scale training of the Kachin Levies began in August 1943 when a V Force team arrived, followed by an American advisory team of eight officers and 40 sergeants, including radiomen, cryptographers, and medics. The Americans went on to raise their own Kachin Rangers near Myitkyina in 1944. When General Joseph Stilwell's Chinese X Force began its advance to cover construction of the Ledo Road, forces from Fort Hertz pushed south on Stilwell's left flank, capturing Sumprabum and then pressing toward Myitkyina before linking up with X Force.

From August 1942 to August 1944, Fort Hertz was sustained entirely by airlift. Every bullet, every sack of rice, every roll of bandages arrived by plane on the same airstrip that served as an emergency landing ground for aircraft flying the Hump, the hazardous air route over the eastern Himalayas that carried supplies from India to China. Pilots who lost engines or ran low on fuel over some of the highest terrain on earth knew that Fort Hertz offered the only alternative to a crash landing in trackless mountains. A radio beacon navigation checkpoint was eventually established at the site, a tiny electronic lifeline in an ocean of peaks. The fort's dual purpose, as both a forward military base and a waypoint for desperate aviators, made it disproportionately important for its size. It was a pinprick on the map that kept an entire corridor of the war functioning.