I wasn't too concerned about the whole aluminum thing until I found out that the M-113 APCs could MELT.
As a tank gunner at Ft Knox in the late 1960s, I was once tasked with putting on an impressive display of tracers bouncing off the side of one of the earlier M59 [steel armor, but no better protection] personnel carriers as part of a firepower display for visiting West Point cadets. Trouble was, the .30 Browning we used as a co-ax machinegun just chewed right through the side...and right out the other side.
We finally got the job done, by digging a ditch with a dozer-blade equipped tank, then dropping the far-side track of the target vehicle into the ditch, which slanted its *armor* at about a 45º angle. That, plus a loading of all-tracer instead of the usual mix of 1 tracer and 5 rounds of ball, let us bounce tracers away into the dusk, about 3000 of them, in cheery little 30-round bursts.
The idea was for the impressive display of what a tank could do- that was their intro- was to tip the scales for some of them to pick Armor as their commissioning branch. The close of the demo was a shoot by a 5-tank platoon, *just like the ones they'd get to be leading as a newly minted *butterbar* armor Second Lieutenant.
We got to talk to them after the shootemup, and most of them weren't all that impressed. But after showing them all the effort it had taken for us to keep from sawing our targets in half, they seemed a whole lot less interested in becoming Mech Infantry platoon leaders. Yeah, we got a couple of good ones out of the deal....
Part of the idea behind the aluminum armor of the M113 series was to allow it to float, the US Army not having any vehicle in its inventory that was amphibious since the WWII DUKW amphib 2½-ton truck was phased out of the system [[and we STILL don't have one!] The sacrifice in protection that resulted was made clear to me when one of our M577 *highboy* command post vehicles in the field suffered a hole through its side when an overenthusiastic crewman was chopping down surrounding trees with an axe for concealment. The gash was about as long as the axe blade was wide, and on the outside, about a half-inch in width. Inside it was only an eighth of an inch or so, though inside the darkened interior it as cheerfully let light stream in as it would have let in water had they tried to swim the thing.
Neither was I real thrilled about the gas tank arrangement in the M113, a plastic bag *bladder* full of gasoline behind the driver inside the aluminum *armor* wall of the vehicle. The old M113 *Bucket* personnel carriers left a lot to be desired....