Field Marshal Earl Roberts. Both of these campaigns, Petre surmised, were Napoleon's greatest achievements: never again did he organize so great a campaign, nor did his political or military power reach such heights. Similarly, his Napoleon & the Archduke Charles; a history of the Franco-Austrian campaign in the valley of the Danube in 1809 reflected the dearth of English language material on the subject. For Petre, the campaign was of particular interest as the one of two campaigns in which Napoleon was opposed by arguably his most able continental opponent. In 1809, that opponent was the Archduke Charles, Duke of Teschen; the other campaign, in Italy 1797, that opponent was Dagobert Sigmund von Wurmser. His son Roderick assisted with the map-making. The volume entered three reprints–1916, 1976, 1989—and a second edition in 1991, reprinted in 2001, reflected the ongoing fascination with the Napoleonic wars. Both Napoleon's last campaign in Germany, 1813 and Napoleon at Bay 1814, were translated immediately into German, and both had 1970s reprints. In Napoleon's Last Campaign, Petre posits that the Emperor Napoleon abandoned the guiding principles of his previous success, which lay in his relentless pursuit of his opponent's main army. In the Saxon Campaign, Napoleon lost sight of his primary objectives, becoming mired in secondary achievements. Petre noted also the vast increase in sheer numbers, on both sides of the contest, and predicted that in terms of numbers, "we must wait for the wars of tomorrow to see those numbers exceeded." World War I interrupted his work as a military historian; he was recalled from retirement to work in the Finance office of the Munitions Ministry. On 26 March 1920, he was appointed Officer of the Order of the British Empire. Petre wrote a two-volume history of the Norfolk Regiment, the second volume of which was published a month before his death. In addition, he also wrote histories of the Royal Berkshire Regiment (Royal Berks), the 1st Gurkha Rifles, and the Scots Guards in the Great War 1914–1918. His regimental histories also included The 1st, King George's Own, Gurkha Rifles-The Malaun Regiment, 1815–1921. Petre also wrote two books on South America, responding to the need for investors to find additional information in a convenient form in English. In it, he maintained, he simply collated information and in his tour of the country he remained on what he called "the beaten tracks", principal cities, and the