The M-1 uses 'Chobham armor, which
for the town in England where it was developed.
The armor consists of 2 steel plates set at least 1 ft. apart,
w/ a steel honey-comb shaped matrix in between.
When a shaped-charge anti-tank round hits the armor,
its molten metal slug is channeled outward by the
honey-comb matrix, causing a cascade effect
that disperses the slug's energy.
Ceramic material in the matrix also negates the effect of the slug.
This is the key, because most anti-tank rounds
a based on
the principle of applying the weapons energy to a small point.
The M-1 was originally going to be a relatively light MBT,
but the Chobham armor is best when it is a certain thickness.
To give the tank the best protection, the thickness
of the armor had to be increased, which was
controversial because of it increased every
thing from fuel consumption to its ability
to be flown on the Armys transports.
Later models of the M-1 had Depleted Uranium
added to the armor to make it even stronger.
Though the Army brushed aside concerns about the
armor's low-level radioactivity during the 80's,
the DU armor is now a suspect in the cause
of the Gulf War Syndrome which has
caused various illnesses in veterans of the war.
Additional protection can be obtained by the
use of reactive armor over the Chobham.