Complex sentence: The 5 inch HVAR was a reliable standby; sturdy Soviet-built armor proved resistant to the HVAR's punch, which led to a new 6.5 in (16.5 cm) shaped charge antitank warhead being developed.
Split into simpler sentences: The 5 inch HVAR was a reliable standby; however sturdy Soviet-built armor proved resistant to the HVAR's punch. This led to a new 6.5 in (16.5 cm) shaped charge antitank warhead being developed.