my @split_arr = map { [ split /_/, $_, 3 ] } @array;
my @sorted = sort { $a->[2] <=> $b->[2] } @split_arr;

##</code><code>##

my @split_arr;
for ( @array )
{
   my @split_elem = split /_/, $_, 3;
   push @split_arr, \@split_elem;
}
my @sorted = sort { $a->[2] <=> $b->[2] } @split_arr;