<p>Guidance system from a Minuteman III nuclear long-range ballistic missile, on display at the Smithsonian Air and Space Museum in Washington, D.C.
</p><p>After World War II, the United States seized a number of Nazi German rocket scientists and V-2 rockets.  The U.S. quickly realized that rockets might be the wave of the future, for a rocket would allow the United States to lob nuclear weapons anywhere it wanted in the world without leaving home.
</p><p>The first American intercontinental ballistic missile (ICBM) was the Atlas.  It was ballistic, because it reached outer space before falling back to earth.  It was interncontinental, because it could reach Europe or Russia.  Manufactured by Convair (a division of General Dynamics), it was a liquid-fueled rocket.  Development began in 1951, and the first flight occurred on November 28, 1958. The Atlas was deployed on October 31, 1959, and the last one retired on April 12, 1965.
</p><p>The Titan I was the second ICBM developed by the United States.  Work began in January 1955, with a first flight on February 6, 1959.  It was almost identical to the Atlas, although it had more lifting power, was more reliable, and its toxic, unstable propellants were stored in tanks rather than in the rocket itself.  It was retired in June 1965.
</p><p>Titan II was the successor to the Titan I.  Work began in June 1960, first flight was in December 1961, and it was retired on May 5, 1987. Like the Titan I, it used toxic, unstable liquid fuel.  But it stored the fuel in the rocket, making it launchable within 60 seconds.
</p><p>The U.S. Air Force, however, wanted a solid-fuel ICBM -- which was safer -- and a more accurate one.  It also wanted a missile which could be fired from underground.  The Atlas, Titan I, and Titan II all had to be raised above-ground due to their toxic exhaust.
</p><p>Lt. Colonel Edward Hall began developing the Minuteman in 1957, with first flight in February 1961.  It was so flawless in performance that it was deployed almost overnight (in 1962).
</p><p>But the key to the Minuteman was the on-board computer.  Developed by the Autonetics division of North American Aviation, the Autonetics D-17 was a digital computer which stored commands on a radiation-hardened magnetic disk.  In the seconds prior to flight, an inertial internal guidance system was aligned and gyroscopes spun up and aligned.  An Autonetics Field Artillery Data Computer (the M18 FADAC) performed most of the basic functions of flight control.  But the fine-tuning of the flight (engine throttling, fin maneuvering, exhaust vane maneuvering, etc.) was controlled by the D-17.  The last Minuteman I was decommissioned in February 1969.
</p><p>Design work on Minuteman II began in February 1962.  First flight occurred on September 24, 1964, and it was deployed in February 1966.  Minuteman II featured a titanium (not steel) nozzle, which lightened it and added range. The second stage rocket engine was entirely new, with a single, non-swivelable nozzle (not four nozzles). It used injections of freon to control the way the exhaust flowed from the nozzle as a means of aiming the rocket.
</p><p>The new D-37C on-board computer was the first to use semiconductors in a military application.  The new computer had vastly enhanced memory, which enabled it to hit any one of a number of targets.  This meant that each missile could be aimed at upward of 10 to 15 targets, rather than just one.  A new internal guidance system was also installed, as well as a pendulous integrating gyroscope.  Minutemn II was three times more accurate than Minuteman I!
</p><p>Design work on Minuteman III began in 1966, first flight was on August 16, 1968, and it was deployed in December 1970.  Although the first and second stages were unaltered, the third stage was radically redesigned.  A new rocket engine was fluid-injected, which provided even finer control over thrust and maneuverability.  With less weight, it carried a much-enhanced payload that included multiple warheads (multiple independently-targetable re-entry vehicles, or MIRVs)  for the first time, as well as anti-detection payloads (like decoy warheads and anti-radar chaff).  Each warhead could carry three bombs.  Each warhead had its own liquid-fuel propulsion system that could be used to adjust their trajectory.
</p><p>A new flight computer, the Autonetics D37D, is a 16-bit high-speed microprocessor.  The inertial guidance system remains the same as in the Minuteman III.  Beginning in 2000, the D-37D was slowly replaced throughout the Minuteman III fleet with the new NS-50 missile guidance computer (MGC).  It is highly classified.
</p><p>Minor reliability, engine, and fuel upgrades were continuously made during the Minuteman III's production run between 1970 and 1978. In 2008, the U.S. Air Force said it would keep the Minuteman III operational until 2030.  The MX (or "Peacekeeper") missile was to have replaced Minuteman III in the late 1908s, but it was retired in 2005 as part of START II treaty agreement.
</p><p>A total of 450 Minuteman III missiles are currently in service.  They are based at Warren Air Force Base in Wyoming, Minot Air Force Base in North Dakota, and Malmstrom Air Force Base in Montana.
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About one Minuteman III is test-flown each year to ensure reliability.
<a rel="nofollow" class="external text" href="https://www.flickr.com/people/23165290@N00">Tim Evanson</a> from Cleveland Heights, Ohio, USA
CC BY-SA 2.0
<a rel="nofollow" class="external text" href="https://www.flickr.com/photos/timevanson/7275763010/">Minuteman III guidance system - Smithsonian Air and Space Museum - 2012-05-15</a>