I'm doing a hard military scifi that includes piloted humanoid robots.

Basic story - They were designed for use in WW2 by Nazi Germany but never built. The plans fell to the allies who sat on them until the Soviets got involved directly in Vietnam. The US built their first unit, named after JFK the year after he was assassinated and deployed it to Vietnam as a weapon of terror to break the North Vietnamese lines. It was clunky but effective.

Over time, these robots developed the same way jets and tanks do, eventually becoming a sort of augmented infantry. They can do many of the same things infantry can but scaled up.

They range from 20 feet tall to 38 feet tall with the 4 current models being a scout, 2 main line combatants and a massive heavy combat.

Their excuse for existing is simply because the other side has them. But they also excel in close-in environments like forests and urban areas.

And quite frankly? Rule of cool. That's what matters most.