In 1943 the 25th Infantry Regiment was created as part of the Patagonia Group. It was first headquartered in the town of Las Heras, Santa Cruz. In December 1943 the town of Puerto Deseado became the barracks of the 25th Regiment. On 31 August 1943 the town of Sarmiento, Chubut became the long term barracks of the 25th Regiment. In the mid-1970s the 25th Regiment deployed officers and other ranks in the fighting taking place in Tucumán Province between military/police units and left-wing guerrillas/radicals. The 25th Regiment was the sole unit of the Argentine Army to take part in the amphibious landings that took place in the Falkland Islands on 2 April 1982, as part of Operation Rosario. A platoon of the 25th Regiment was detached to clear the obstructions on Stanley Airport in the form of abandoned vehicles and concrete blocks. During the Falklands War, the Commanding Officer, Lieutenant-Colonel Mohamed Ali Seineldin was entrusted with the defence of Stanley Airport. The 25th Regiment's C Company formed outposts at Goose Green and San Carlos, along with part of the 12th Infantry Regiment. C Company suffering heavy casualties on Darwin Ridge and Goose Green Airbase, and forced the British attackers to withdraw twice in the battle before the Argentines surrendered. During the British landings on 21 May, the 12th Regiment platoon under Sub-Lieutenant José Alberto Vásquez shot down 2 Gazelle helicopter-gunships, while at Fanning Head the majority in the 25th Regiment platoon under Sub-Lieutenant Roberto Oscar Reyes were able to successfully evade encirclement by British SBS Commandos. The 25th Regiment received Commando training in February/March 1982, according to the book 9 Battles To Stanley. British Warrant Officer Nick Van Der Bijl, who interviewed key captured Argentine officers in the fighting has written: Van Der Bijl even alleges that a mutiny was at one stage plotted, to replace Brigadier-General Mario Menéndez with Colonel Seineldín of the 25th 'Special' Infantry Regiment. In recognition of their role in the Falklands War, the regimental battle flag was awarded the "Medalla de Campaña" of the Argentine Army, "To the flag that fought in the South Atlantic" of the Santa Fe Province and the Medal of the Municipality of Sarmiento. In all, 35 officers and other ranks were decorated, including Lieutenant Roberto Néstor Estévez, a platoon commander during the Battle of Goose Green.
