Pvt Robert L Dickert 42114981 Co. A 31st Bn 2nd Pl. Camp Croft, SC
The fact that his service number starts with a 4 indicates that he was a late-war draftee.The number (2) indicates that he hailed from either New York or New Jersey.
Co means Company so he was in Company A--which is always in the first Battalion (1st Bn)Each company is broken down into sections called platoons.He was in the 2nd Platoon.I would have to believe that the (3) in "31st Bn" is a typo as there are not 31 Battalions in any subdesignated military unit.Generally four (4) at most.
What is curious is that there is no IDENTIFIABLE organization, as in a numbered Regiment or Division.
2nd Pltn, A Co. 1st Bn could well apply to any one of hundreds of Army Regiments.
This is a stateside unit (possibly where he did his basic training), as there would be an APO included in the address if it was for an overseas mailing.