31354 Federal Infantry in Frock Coat Advancing at Right ShoulderMilitary frock coats were introduced during the Napoleonic Wars to French line infantry and Prussian Landwehr troops. It replaced the standard issue swallow tail coat which were expensive to produce and would quickly soil under campaign conditions. A loose fitting single breasted frock coat was cheaper to manufacture and more practical for campaigns. By the 1840s, frock coats were regulation for the American army with officers issued navy blue frocks