Complex sentence: His Plan 1919 for a fully mechanised army was never implemented in his lifetime, and after 1918 he held various leading positions, notably as a commander of an experimental brigade at Aldershot.
Split into simpler sentences: His Plan 1919 for a fully mechanised army was never implemented in his lifetime. After 1918 he held various leading positions, notably as a commander of an experimental brigade at Aldershot.