block other officers from being promoted. Some statutory limits under the U.S. Code can be waived in times of national emergency or war. Three-star ranks may also be given by an act of Congress but this is extremely rare. Retirement Other than voluntary retirement, the statute sets a number of mandates for retirement. Lieutenant generals must retire after 38 years of service unless appointed for promotion or reappointed to grade to serve longer. Otherwise, all general officers must retire the month after their 64th birthday. However, the Secretary of Defense can defer a three-star officer's retirement until the officer's 66th birthday and the president can defer it until the officer's 68th birthday. General officers typically retire well in advance of the statutory age and service limits, so as not to impede the upward career mobility of their juniors. Since there is a finite number of three-star slots available to each service, typically one officer must leave office before another can be promoted. Maintaining a three-star rank is a game of musical chairs; once an officer vacates a position bearing that rank, they have 60 days to be appointed or reappointed to a position of equal or higher importance or involuntarily retire. Historically, officers leaving three-star positions were allowed to revert to their permanent two-star ranks to mark time in lesser jobs until statutory retirement, but now such officers are expected to retire immediately to avoid obstructing the promotion flow. History On February 28, 1855, President Franklin Pierce nominated Winfield Scott to be breveted lieutenant general, effective March 29, 1847, as an honor for his capture Veracruz and San Juan de Ulúa, during the Mexican–American War. The grade was re-established by a vote in House of Representatives on 1 February 1864, with 96 for and 41 against. On June 1, 1888, the rank was merged with General of the Army and discontinued. Modern use An Army or Marine Corps lieutenant general typically commands a corps-sized unit (20,000 to 45,000 soldiers for an Army Corps and a similar number of Marines for a Marine Expeditionary Force), while an Air Force lieutenant general commands a large Numbered Air Force consisting of several wings or a smaller USAF Major Command (MAJCOM) such as the Air Force Special Operations Command or the Air Force Reserve Command. Additionally, lieutenant generals of all services serve as high-level staff officers at various major command headquarters and The Pentagon,