This is quoted from the military regulation on criteria for the award:
"The Presidential Unit Citation is awarded to units of the Armed Forces of the United States and co-belligerent nations for extraordinary heroism in action against an armed enemy occurring on or after 7 December 1941. The unit must display such gallantry, determination, and esprit de corps in accomplishing its mission under extremely difficult and hazardous conditions as to set it apart and above other units participating in the same campaign. The degree of heroism required is the same as that which would warrant award of a Distinguished Service Cross to an individual. Extended periods of combat duty or participation in a large number of operational missions, either ground or air is not sufficient. This award will normally be earned by units that have participated in single or successive actions covering relatively brief time spans. It is not reasonable to presume that entire units can sustain Distinguished Service Cross performance for extended time periods except under the most unusual circumstances. Only on rare occasions will a unit larger than battalion qualify for award of this decoration."
"The emblem is worn by all members of a cited organization and is considered an individual decoration for persons in connection with the cited acts and may be worn whether or not they continue as members of the organization. Other personnel may wear this decoration while serving with an organization to indicate the unit has been awarded the Presidential Unit Citation."