At the turn of 1775-6, Ferguson was back in Scotland. In April, he went to London to try to interest Lord Townshend in his rifle design. He eventually succeeded, and by May was at the Tower of London, supervising the making of trial models and taking part in tests before leading generals and dignitaries. The trial on 1 June received full coverage in the Annual Register. On 4 July, while the Rebel Continental Congress voted for independence and sent its declaration for publication, Ferguson was in Birmingham supervising the manufacture of the first 100 Ferguson Rifles made for military service. Ferguson presented the King with sketches and a description of the rifle. Via Major Cuyler, Howe's ADC, he received the General's backing, and petitioned the King to command an experimental rifle corps in the Colonies. The rifle patent was approved on 2 December 1776, and he also received private orders from individual officers and the East India Company for rifles. These helped his finances: he had got into debt through paying for the early models and trials from his own Captain's pay, and had borrowed money from relatives to pay for the patent. He was already working on a small field-gun. In January 1777 he received permission from Townshend and General Harvey to train 200 recruits at Chatham for his experimental corps. However, with news of defeats at Trenton and Princeton, he was ordered to make ready more quickly, with only 100 men. He officially received his command on 6 March. His instructions were that at the end of one campaign, he and his men were to be returned to their original regiments, unless Howe specified otherwise. In March 1777, Ferguson and his corps sailed on the Christopher to New York, where they arrived on 26 May. The experimental field piece blew up in its first test, having been sent out with the wrong size of ammunition. However, the corps - uniformed in the green cloth which had been sent out with them - saw some action in New Jersey. They took part in the expedition to the Chesapeake, where Howe, a light infantry enthusiast, was impressed with them. He assured Ferguson that he intended to expand the rifle corps. Unfortunately, events at Brandywine on 11 September 1777 ended these prospects. Ferguson's Corps performed well in the battle, fighting alongside the Queen's Rangers, under James Wemyss. Ferguson had the chance to pick off a important-looking Rebel officer, but declined to do so for reasons of honour. He was later told in hospital that the officer may have been Washington, but this cannot be proven with certainty. (Knowing the sense of humour some medics have, it may have been a wind-up...) Ferguson, at any rate, believed it was, and wrote, "I am not Sorry that I did not know all the time who it was". There were graver matters on his mind. Moments after the alleged encounter with Washington, a musket ball shattered Ferguson's right elbow-joint. He spent the winter in Philadelphia, under threat of amputation. He endured numerous unanaesthetised operations to remove bone splinters which repeatedly broke open his wounds. In November, he also received news of his father's death in June. Yet in letters home, he bravely made jokes about his operations.