The M48 was a redesign incorporating many of the lessons learned from the M46 and M47 series tanks, with production starting in 1952 and running through 1959.  Some of the lessons.  Not all, certainly.

They were still powered by gasoline engines, and the early versions had a range of only 70 miles.  They didn't get diesels until 1968.  Heh. Lit up like a barbecue and had no legs, to boot. According to the info I found while poking about, in the addition to the Marine users, the 1/77th Armor, the owner of the tank in the original post, operated near the DMZ, with two other Army battalions using the tank in Vietnam - 2/34 Armor in the Delta and 1/69 Armor in the Central Highlands. They were appreciated by the infantry, and 1/69 AR actually had a tank-on-tank fight with PT-76's at Ben Het.

The M48 was designed to fight WWIII in Europe.  When they were first deployed, the M48-A3 had a state-of-the-art fire control system - well, for the 60's anyway.  It was a mechanical fire control computer - you determined your range-to-target with a stereoscopic range finder (those protrusions on the side of the turret), which used a split image - like old SLR cameras. Turning a hand-crank on the range finder would move mirrors that were housed in those projections on the turret - the farther apart you could get those, the more accurate your range is)  until the double-image in the range finder merged into one image.   Since you know your base distance (that between the mirrors), you can now do a little trig based on the mirror angles to determine a range.  Range was displayed on a range indicator, and also fed to the ballistic computer by a rotating shaft and gear system. The ballistic computer was a collection of gears and cams-- like the computer in the USS John Rodgers (if rather smaller!) --which had a handle so that the gunner could select the type of ammunition that was to be fired. Each type round has a different muzzle velocity, and therefore the computer has a different cam for each round. The computer would take the range data, merge it with the velocity data, and via a set of rotating shafts, supply this information to the gun's super-elevation mechanism, resulting in the gun being elevated above the gunners line of sight sufficiently for the round to overcome the downward pull of gravity on its way to the target, all while the Gunner was still visually locked onto the target. 

The precision of this  fire control system was pretty much wasted in Vietnam - where most engagements were the tank equivalent of hand-to-hand, which led to some adaptations in how vehicles were crewed.  In Vietnam it was fairly common to take the gunner out of the turret and put him on the back deck with an M16 or M79 grenade launcher for close-in protection. This also afforded him some protection from mines, and indeed the tank commander and loader often rode on the turret roof or the hatch lips when mines were expected - though if you had to hit a mine while riding in a vehicle, the M48 was a much better choice than the other options   As the pictures show, apparently most M48's in Vietnam had the commander's .50 cal. mounted on top of the cupola on that field expedient pintle. This location gave a better field of fire, was faster to reload, and less prone to jamming than when the M2 was placed on its side inside the armored cupola. I'm thinking the TC still felt pretty nekkid shooting the .50. 

The Germans still had some M48s (muchly upgraded) in service when I was in Germany in the early 80's, serving with their reserve forces, and they can still be found around the world.

I've got one more post about the M48, when I get around to it.

H/t to FAS for the description of the fire control system.