Dear Mr. O’Neil,
Thank you for posting your request on History Hub!
SGT (T) indicates a temporary promotion to Sergeant. In 1951, the rank of Sergeant was indicated by three chevrons and one rocker. Chevrons were olive drab on dark blue. More more information about enlisted rank structure and insignia during this time period, please see the following:
- https://history.army.mil/html/books/non_commissioned_officer/CMH_70-38.pdf (page 296)
- https://history.army.mil/html/museums/uniforms/survey_uwa.pdf (page 87)
We hope this information is helpful.