FMC responded with two proposals; two versions of the aluminum T113 - a thickly and a more thinly-armored one, along with the similar but mostly steel T117. The thickly-armored version of the T113 - effectively the prototype of the M113 - was chosen because it weighed less than its steel competitor, whilst offering the same level of protection. An improved T113 design, the T113E1, was adopted by the U.S. Army in 1960 as the "M113". A diesel prototype, T113E2, was put into production in 1964 as the "M113A1", and quickly supplanted the gasoline-engined M113. In 1994, FMC transferred the M113's production over to its newly formed defense subsidiary, United Defense. Then in 2005, United Defense was acquired by BAE Systems.