William Simpson arrived off the Crimean peninsular on November 15 and could hear distant firing. While he had missed the early battles, he was able to record the events before Sebastopol. He made numerous acquantances who helped him with details for his pictures, but he was also struck by the plight of the common soldiers, "miserable looking beings...covered with mud, dirt, and rags," he wrote. He hobnobbed with many officers including Lord Raglan and Captain Peel; he also met Roger Fenton who took his photograph. In May, 1855, Simpson accompanied Raglan on the expedition to Kertch which was captured on the 24th, but was back in time to observe the first attack on Sebastopol in June. On the night of the 17th, he crawled out of a trench to view the attack. He wrote, "It was a wild orchestra of sound, never to be forgotten." He was still at the front when the city finally surrendered, and he quit the Crimea in the autumn of 1855.

Throughout his time at the front, he would send back his water-colors to London where the lithographers of Day & Son would transfer them to stone. Simpson was paid 20 pounds for each picture. For the color, a separate stone was used for each tone. Colnaghis exhibited some of the water-colors including a show at the Graphic Society in February 1855. The first advertisements for the lithographs appeared in May 1855 and in the following month, a second series was announced. In all, the Colnaghi's produced two large portfolios containing over eighty lightographs entitled The Seat of the War in the East. Two thousand copies of the complete set were produced. Simpson dedicated the series to Queen Victoria whose patronage he enjoyed for the rest of his life, and he was a frequent visitor to Windsor Castle and Balmoral. So popular were his pictures that he became affectionately known at 'Crimean Simpson'.