In 1943, the US-Army needed cheap, light and easy to use divices for their wounded soldiers. The Eames couple came up inspired by the furniture of Alvar Aalto with those leg splints.
Before the Eames even started to invent furniture, they were already pretty wealthy and were able to build tones of prototypes. The second thing what made them so famous is the fact, that they were one of the first who were testing there own furniture in matter of long life lastings products. So they build huge kind of laundry machines to test their furniture.
http://ablersite.org/2010/05/17/adaptation-part-i-how-the-eames-chair-came-from-leg-splints-and-why-disability-studies-isnt-just-identity-politics/
http://vitrablog.co.uk/page/12/
Together with Zenith Plastics, the Eames invented the upper shown chairs for a challenge called „Low Cost Furniture Design“ at the Museum of Modern Art. One seat, many different bases e.g. "H-Base, La Fonda, Eifeltower, Wood, Alu, Rocker….".
DSW=Dining Height Side Chair Rod Base
vintage EA 117 notice the fourstar-base, usually they have five.
http://www.smow.de/vitra/dsw.html
http://eamesdesigns.com/catalog/seating/