On the outbreak of war with Russia in 1854, Morris was appointed Deputy Assistant Quartermaster-General in the Cavalry Division of the Army of the East, leaving for Turkey in April. While at Varna he contracted cholera, and did not participate in the initial invasion of the Crimea, only joining the army besieging Sebastopol in October, where the 17th Lancers were also present as part of the Light Cavalry Brigade. Their commanding officer, Lieutenant-Colonel John Lawrenson, had been sent home sick, so when Major Augustus Saltren Willett died of cholera on 22 October, Morris, as senior captain, was entitled to take command of the regiment. Despite being weakened by his illness and a "complete stranger" to the men of the 17th, he chose to exercise this right rather than remain on the staff. He was therefore in command of the regiment at the Battle of Balaclava on 25 October 1854, still wearing his staff-officer's frock-coat and cap and riding his charger "Old Trumpeter".