Interesting question!
Mexico entered WWII with a bang. Well, two bangs. On May 13, 1942, a U-boat torpedoed a Mexican oil tanker. 13 sailors drowned. Days later, a second tanker was sunk, with more loss of life. The Germans flatly refused a repayment demand President Manuel Avila Camacho (no, not the guy from Idiocracy). So Mexico went to war.
For about a year, nothing happened. Mexico's armed forces were in disarray and unready for overseas service. Impoverished Mexico had very few resources to spare for an expeditionary force.
All that changed after FDR personally travelled to meet with President Camacho in Monterrey during April 1943. FDR encouraged Mexico to take an active, offensive role in the war effort. The Allies were going on the offensive, and a Mexican troops had real and symbolic value for the Allied cause.
Intially, President Camacho waffled. But he eventually made up his mind: Mexico would fight.
On November 13, he declared that Mexican troops would take part in the wat, provided they would be under Mexican command. It wasn't dissimilar with Blackjack Pershing's effort to keep the American Expeditionary Force from being split up in 1917.
With Mexico's army unready and under-equipped, the task of fighting the war would fall to Mexico's fledgling air force, the Fuerza Aérea Mexicana (FAM). The small FAM had already been bolateed2 by the gift of American planes: Douglas A-24B Banshee (a USAAF variant of the SBD Dauntless dive bomber), North American B-25 Mitchell medium bombers and Consolidated PBY Catalina flying boats. Initially the FAM had preoccupied itself with coastal defense, with some success. Flying a North American AT-6 Texa, Major Luis Noriega Medrano had successfully attacked the submarine U-129 on July 5th, 1942.
The task of getting the FAM ready to go on the attack fell to the service's most seasoned officer: Colonel Antonio Cardenas Rodriguez. The globetrotting colonel was a minor celebrity in Latin America for his goodwill flights across the country. Even more importantly, he was a combat veteran who had flown combat missions over North Africa with the American 97th Bombardment Group.
By July 1944, Rodriguez's detachment had assembled volunteers from all over Mexico, including a Mexican-American paratrooper and a former cavalryman turned pilot. Together, they formed the Grupo de Perfeccionamiento de Aeronáutica or Aeronautical Training Group. These pilots and ground crews headed to the United States for training. After qualifying on the Curtiss P-40 Warhawk in Texas, the pilots went to Idaho, then back to sunny Texas, to fly the big Republic P-47D Thunderbolt. The Mexican aviators liked the big fighter, fondly dubbing it the * "Peh-Cua," short for the Spanish cuarenta y siete, or forty-seven.
But the Peh-Cua could be handful for young pilots. Pilot training in WWII was incredibly dangerous and the Mexicans didn't get off unscathed. On January 23rd, 1945, Second Lieutenant, Cristoforo Salido Grijalva flipped his P-47 while taking off on a muddy taxiway. Trapped in the cockpit, the young pilot drowned before frantic ground crews could rescue him. On March 10th, 1945, while the unit was doing its final workups before shipping out, another disaster struck. While chasing an aerial gunnery target being towed by another aircraft, Lieutenant Javier Martinez Valle struck the cable, lost control and crashed. The two men wouldn't be the last Mexican fliers to fall.
Although there had been thoughts of sending the Mexicans to fly with the Brazilian squadron already fighting in Italy, President Camacho had another idea. He suggested to FDR that they be sent to the Philippines to take part in "the liberation of a people for whom it is felt a continuity of idiom, history and traditions." FDR agreed.
By now, the unit had been declared ready for action and dubbed the Fuerza Aerea Expedicionaria Mexicana (FAEM) or Mexican Expeditionary Air Force. It had ground crews, support staff, and the Escuadrón Aéreo de Pelea 201 or 201st Air Fighter Squadron. On February 22, 1945, the FAEM was given its battle flags and serenaded by two marching bands before putting on an airshow for the newsreel cameras. After a few more weeks of training, the FAEM boarded a transport in San Francisco on March 27th, 1945. After weeks of sailing, they arrived in Manila Bay.
The FAEM was a latecomer to the battle for the Philippines. Filipino and American guerillas had been fighting since 1942. In October 1944, American assault troops had waded ashore, making good on MacArthur's pledge: "I shall return." The following days had been filled with hard fighting in field, jungle, and in the battle-scarred streets of Manila itself. The campaign was still far from over, as the Mexican airmen soon realized. At their new base at Porac, the Mexicans could hear the sound of rifles and artillery from the nearby fighting.
In keeping with President Camacho's requirements, the Mexicans were given a fair bit of latitude. They handled their own administration and were given their own area of the base. Operationally, they'd be under the control of the 58th Fighter Group of the USAAF's Fifth Air Force.
On May 17th, a little over two weeks after arriving in the Philippines, the Mexican pilots flew their first missions. To orient the Mexican pilots, the other 58th Fighter Group squadrons took them under their wing and had individual Mexican pilots fly missions with them. Once they had gotten a feel for things, the 201st could fly missions on its own. Since the Americans had established total air superiority over the islands by early 1945, the Allied air forces were focused on ground attack.
In mid-May 1945, the 201st started flying missions on its own. Their first targets were Japanese troops, artillery, and bases east of Manila. The GIs of the 25th were fighting a bitter war against the Japanese on the large island of Luzon.
May 17, 1945, the 201st began flying combat orientation missions, with its pilots assigned to various other squadrons. Shortly thereafter, however, the so-called Aztec Eagles started flying missions as a unit. Their initial targets were buildings, vehicles, artillery and enemy concentrations in the Marikina watershed east of Manila, where the U.S. 25th Infantry Division was encountering fierce resistance.
Until the end of the war in August 1945, the 201st was flying missions nearly every single day. Pilots routinely flew two combat sorties a day, taking off early in the morning to bomb and strafe, then returning to base for an afternoon strike. In early July and August, the Aztec Eagles made their longest missions ever. Im Jul y they launched a long-range fighter sweep over Formosa (now Taiwan), followed by dive-bombing attacks on the island a month later. With the IJAAF and IJNAF destroyed, the Azetc Eagles never had the chance to fight or kill a Japanese aircraft. All in all, the 201st flew 96 missions and a total of 791 combat sorties, at the cost of five pilots lost on combat operations - most of them in crashes (one shot down, one crashed, three ditched due to fuel starvation and were lost).
What about other Latin American countries? As you know, Brazil's army and air force both fought in Italy, making the biggest and most significant Latin American contribution to the Allied cause.
Other Latin American powers entered the war on the Allied side mostly because they wanted to fight each other, rather than because because they wanted to fight the Nazis. If that sounds strange, let me explain.
Bolivia and Peru, for example, received American weapons through Lend-Lease. Both countries had an axe to grind with Chile, who had dealt them a humiliating and economically-ruinous defeat sixty years before during the war of the Pacific. This worried Chile quite a bit, and the Bolivian-Peruvian threat was one reason why Chilean President Ríos ended Chile's relations with German and Japan in January 1943. This made Chile eligible for the Lend-Lease program and let it get loans to rebuild its faltering economy.
Ecuador was also worried about a rematch of the 1941 Ecuadorian-Peruvian War, which it had lost to Peru. This was one reason why the Ecuadorians sought (and got) their own Lend-Lease deal by throwing in their lot with the Allies.
Sources:
"World War II: Mexican Air Force Helped Liberate the Philippines"
"The Mexican Expeditionary Air Force in World War II: The Organization, Training, and Operations of the 201st Squadron" by José G. Vega Rivera