Complex sentence: It is the U.S. Army's intention that the BCT Ground Combat Vehicle Program will replace the M2 Bradley and M113 with the GCV Infantry Fighting Vehicle by 2018, while the M3 Bradley could later be replaced by future variants of the GCV.
Split into simpler sentences: It is the U.S. Army's intention that the BCT Ground Combat Vehicle Program will replace the M2 Bradley and M113 with the GCV Infantry Fighting Vehicle by 2018. The M3 Bradley could later be replaced by future variants of the GCV.