 Because of his political connections and his mastery of French , McClellan received the assignment to be an official observer of the European armies in the Crimean War in 1855 . Traveling widely , and interacting with the highest military commands and royal families , McClellan observed the siege of Sevastopol . Upon his return to the United States in 1856 he requested assignment in Philadelphia to prepare his report , which contained a critical analysis of the siege and a lengthy description of the organization of the European armies . He also wrote a manual on cavalry tactics that was based on Russian cavalry regulations . Like other observers , though , McClellan did not appreciate the importance of the emergence of rifled muskets in the Crimean War , and the fundamental changes in warfare tactics it would require . 
