U.S.C. § 371) retires is thereafter referred to as a "retired justice". No mention is made, either in section 371 or in section 294 (which does address the assignment of retired justices), of senior justice. In practice, when a circuit or district judge on senior status sits on an inferior court case, the judge is referred to as "Senior Judge" in the opinion, while a retired justice is referred to as "Associate Justice" when doing so. Assignment The rules governing assignment of senior judges are laid out in 28 U.S.C. § 294. In essence, under normal conditions, the chief judge or judicial council of a circuit may assign a senior judge belonging to that circuit to perform any duty within the circuit that the judge is willing and able to perform. A senior district judge can be assigned to an appellate case, and a circuit judge can be assigned to preside over a trial. For courts that do not fall within a circuit, such as the United States Court of International Trade, the chief judge of that court can assign a senior judge of that court to perform any duty within the circuit that the judge is willing and able to perform. In special cases, the chief justice can assign a senior judge to any court. This is referred to as an assignment by designation, and requires that a certification of necessity be issued by the appropriate supervisor of the court. For a circuit or district court, this supervisor is either the chief judge or the circuit justice of the circuit. For any other court, this supervisor is the chief judge of the court. Retired justices can be assigned to any court (except the Supreme Court) that the justice is willing to accept. Theoretically, a retired justice could also be assigned to act as circuit justice for a circuit, but this has never occurred. History In 1919, Congress created the senior status option for inferior court judges. Before that, a judge who reached the age of seventy with at least ten years of service as a federal judge was allowed to retire and receive a pension for the rest of their life; afterward, a judge who qualified for retirement could assume senior status. John Wesley Warrington became the first federal judge to exercise this option on October 6, 1919. At that time, Warrington had been on the bench for ten