Complex sentence: Captain (later Colonel Sir) Alexander Moncrieff, who built on his observations in the Crimean War to improve on existing designs for a gun carriage capable of rising over a parapet before being reloaded from behind cover, created the first widely adopted design.
Split into simpler sentences: Captain (later Colonel Sir) Alexander Moncrieff, improved on existing designs for a gun carriage capable of rising over a parapet before being reloaded from behind cover. His design, based on his observations in the Crimean War was the first widely adopted design.