Complex sentence: The first tanks to go into action, built by Great Britain, were designed from scratch and inspired by but not directly based on the Holt, but the slightly later French and German tanks were built on modified Holt running gear.
Split into simpler sentences: The first tanks to go into action, built by Great Britain, were designed from scratch and were inspired by but not directly based on the Holt. The slightly later French and German tanks were built on modified Holt running gear.