...where they keep IRRs on the hook and bring them back for training--all very informal. USAF has that, I think. Here, in all its boring glory:
http://arpc.afrc.af.mil/dpssc/IRR_Standby_sections.htmBasic Army IRR info, courtesy of Global Security:
http://www.globalsecurity.org/military/agency/army/usar-irr.htmReserve units and may replace Soldiers in Active and Reserve Units. Part of the Army's Ready Reserve, the IRR involves individuals who have had training, served previously in the Active Component or the Selected Reserve (such as a member of an Army Reserve unit), and may have some period of Military Service Obligation remaining. Unlike new recruits, these are seasoned, experienced Soldiers who can contribute significantly to Army readiness. The IRR, as it exists, is mandated by Congress under Title 10 of the U.S. Code. In accordance with implementing instructions contained in Army Regulation 135-91, members of the IRR can be required to join an Army Reserve unit if they are statutorily obligated and have a skill needed by the Army.
Activation is when an Army Reserve Soldier is called to serve in the Army full time. Activation can put you in an Army job within the United States or you may be deployed to foreign soil. Once activated, Army Reserve Soldiers can only serve a maximum of two years active duty.
Presidential Reserve Callup Authority is a Provision of a public law (US Code, Title 10 (DOD), section 12304) that provides the President a means to activate, without a declaration of national emergency, not more than 200,000 members of the Selected Reserve and the Individual Ready Reserve (of whom not more than 30,000 may be members of the Individual Ready Reserve), for not more than 270 days to meet the support requirements of any operational mission. Members called under this provision may not be used for disaster relief or to suppress insurrection. This authority has particular utility when used in circumstances in which the escalatory national or international signals of partial or full mobilization would be undesirable. Forces available under this authority can provide a tailored, limited-scope, deterrent, or operational response, or may be used as a precursor to any subsequent mobilization.Also, there's a difference between officer and enlisted obligations. If you have a commission, and have retired, and collect a pension (in essence, that pension is deferred compensation, which is why you have to pay FEDERAL INCOME tax on it), you are subject to recall at any time, and it is an entirely possible scenario for any officer who is under 60--just depends how bad it gets. It has happened more rarely to those who are older, but it does happen, usually to those with very specialized skills (doctors who can repair screwed up faces, or have a specialty in orthopedics, exotic diseases, thoracic surgery, that kind of thing...dentists who can put together very disfigured kids...or who can take the place here in the US for someone else they need in the sandbox).