Even a small tank force could devastate the 1982 landing vehicles

What threat would a few Sherman Fireflies or Centurions pose to the 1982 Argentine landing force?

A severe one: their guns could destroy the lightly armoured landing vehicles before the marines established a secure foothold.

The Argentine troops came ashore in lightly protected tracked landing vehicles derived from U.S. Marine Corps designs. Sherman Fireflies could have destroyed those vehicles easily, while a maintained platoon of Centurions would have been even more formidable. Losing the transports at the water's edge could prevent the landing force from establishing itself. The counterfactual connects a small land garrison directly to the success or failure of a naval amphibious operation.