Maybe it was field-tested at least…
Here’s what I found on another forum :
“Though the M548’s main purpose was to carry cargo, that didn’t stop some of their crews from improvising in various ways. One of these improvisations was done by Battery G of the 55th Air Defense Artillery Regiment of the 23rd Infantry Division on a M548 nicknamed “Swamp Fox”. This M548 was modified to carry the M55 quad .50 cal AA turret. Because of this modification, the canopy could not be fitted, however, the cabin can and was, along with the extra .50 cal. The M55 turret was an improvement over the M45 turret (seen on the M16), featuring a more powerful generator. The example that Swamp Fox used was fitted with addon shields on either side of the turret. The M55 turret weighs less than 2 tons, likely allowing the vehicle to retain its amphibious capabilities. Not much else is known about the Swamp Fox, however, it’s likely that it was a one-off field modification.”
https://forum.warthunder.com/index.php?/topic/540449-m548-swamp-fox-ditching-the-half-track/
H.P.