The unpack approach used by BrowserUk above is IMHO quite elegant and attractive, not to mention efficient, but a regex-extraction approach offers one further possible advantage: data validation.

c:\@Work\Perl\monks>perl -wMstrict -MData::Dump -le
"my $s = 'abcdefghijklmno';
 ;;
 my $validate = qr{ \A (....) (..) (..) (.....) (..) \z }xms;
 ;;
 my @ra = Suc($s, $validate);
 dd \@ra;
 ;;
 sub Suc {
   my ($DC, $rx_valid) = @_;
   ;;
   my @ra = $DC =~ $rx_valid;
   @ra or die qq{bad format: '$DC'};
   ;;
   return map uc($_), @ra;
   }
"
["ABCD", "EF", "GH", "IJKLM", "NO"]
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Here, the validation/extraction regex is defined separately and passed to the function. Rather than the dummy used in the example code, it can be highly specific to the data. One can imagine a further elaboration in which the passed regex is optional and a default regex is used in the subroutine if no regex is passed:
    my ($DC, $rx_valid) = @_;
    $rx_valid //= qr{ \A default pattern \z }xms;