The U.S. War department has
always pursued a policy of tagging racial organizations.
The nomenclature for 
World War II disignated:

• Army units as #2
• Air Force units as F
   

  
   
   

  The Civil War had given
  birth to the notion; ordinal numbers were used to indicate colored. Many early colored units were organized, then assigned as State or Corp d'Afrique.

  Later, they were redesignated, after the establishment of the Bureau of  Colored Troops, May 22, 1863 under General Order No 143, by order of the Secretary of War. The 1st
  Regimental Kentucky, Heavy Artillery, African Descent 7th CFA H was
  organized. The final designation: 8th US
  Colored Field Artillery H.
  Source: John R. Trowbridge

• 54th Massachusetts Volunteers 
• 55th Massachusetts Volunteers 
• 5th Massachusetts  Calvary 
• 29th Massachusetts Infantry