There are a number of common titles of position and rank which are abbreviated. Except for Dr., they are used only before a person's full name (i.e., at least first and last names); otherwise, the title is spelled out.
Correct: Sgt. Alvin York Fr. Robert Drinan
Prof. William Alfred Dr. Milton Friedman
Incorrect: Sgt. York Fr. Drinan Prof. Alfred
(Abbreviated without first name or initial.)
Correct: Sergeant York Father Drinan
Professor Alfred Dr. Friedman
(Dr. is OK to abbreviate with a last name only.)
Practice for internal correspondence within military commands may differ.
Abbreviations of position and rank include the following.
Professional: Dr. Atty. Prof. Hon.
Religious: Rev. Fr. Msgr. Sr.(Sister) Br.(Brother) St.
Political: Pres. Supt. Rep. Sen. Gov. Amb. Treas. Sec.
Military: Pvt. Cpl. Spec. Sgt. Ens. Adm. Maj. Capt.
Cmdr. (or Cdr.) Lt. Lt. Col. Col. Gen.