This is why a South American country still uses WWII-era tanks
Not every country in the world can afford to buy and operate the latest and greatest armored war machines available on defense markets today, like the M1A2 Abrams or the Leopard 2 main battle tanks.
Some countries opt to refrain from maintaining a fleet of tanks at all, and others, like Paraguay, choose to use refurbished armored steeds from conflicts long past.
As crazy as it may sound, the backbone of the Paraguayan military's sole armored squadron consists of a humble handful of M4 Sherman medium tanks and M3 Stuart light tanks. Both of these vehicles were last fully relevant when Allied forces marched across Europe on their path to victory against the Axis scourge.
Paraguay received its small complement of Shermans in 1980 from Argentina, while the Stuarts were donated by the Brazilian government in the 1970s. By the time the small South American nation received these second-hand vehicles, however, they were already obsolete and outclassed, unable to stand up to anti-tank weaponry or even other armored vehicles anymore.
But in recent years, the Paraguayan army has decided to reactivate its fleet of Shermans and Stuarts, "modernizing" them by installing new engines and replacing the M4's small battery of .30 caliber Browning M1919 medium machine guns with .50 caliber M2 'Ma Deuce' heavy machine guns.
The Sherman was born of a need for a medium-sized tank that was easy to mass produce and deploy overseas in large numbers, swarming larger and more heavily-armored German tanks during WWII. Cheap to produce, and pretty reliable if treated well, the Sherman was a fairly potent killing machine in the hands of tank commanders who knew what they were doing.
The Argentinian military received 450 Shermans from Belgium in the 1940s, putting them through a series of upgrades over the next 30 years that would see these old tanks get larger guns and new diesel engines. A small selection of these Shermans were passed on to Paraguay, though it's unclear whether or not the examples donated were modernized or left in their original configurations.
According to Ian Hogg in his book, "Tank Killing," the Stuart, wasn't exactly very effective at all in engaging German armor. Though it was one of the few light tanks capable of firing high-explosive shells, it was better utilized as a high speed reconnaissance vehicle by British forces throughout the African theater during WWII, with its turret removed to cut down on weight.
Brazil picked up its Stuarts from the United States in WWII, actually shipping them overseas for combat in Italy as part of the Brazilian Expeditionary Force. Upon the end of the war, these tanks were returned to South America by ship and were upgraded in the 1970s. During that decade, Brazil donated 15 Stuarts to Paraguay.
Paraguay can afford to use these older machines in place of newer heavy tanks mostly because the country hasn't seen much war over the past 40-odd years. Currently, the military claims these modernized Shermans and Stuarts will only be used for training purposes, though the endgame of the training is highly suspect, considering that the vehicles in question aren't fit for combat against a decently-armed enemy.
It is possible, however, that these old fighting machines could be eventually used in the long-standing counterinsurgency effort Paraguay has been embroiled in against guerrillas since 2005. Though their hulls would likely be easily destroyed by small anti-tank weapons like the M72 LAW, the armor would still be able to stand up to small arms like pistols and rifles.
Even if Paraguay never uses its tanks in combat, its geriatric fleet will still work in a pinch should the need arise — at least against unarmored and under-gunned enemies.