M113 APC

[nuke11]

Aluminum armor needs to be 3x as thick as it's RHA counter part for the same ballistics capabilities. This is not an exact formula, but will yield a close enough figure.

I believe the front of the M113 is proof against 14.5 mm.

The upper front armor is 38 mm @ 45 degrees and the lower front is 38 mm at 30 degrees.

For a good reference on the M113 family : http://afvdb.50megs.com/usa/m113.html