In December 1853 with the Crimean War waging, he was posted , commanded by his uncle, Lord Clarence Paget. Soon after boarding the ship his uncle made him his "aide-de-camp". In February the Baltic Fleet was anchored at Spithead when Queen Victoria, Montagu's godmother, came to inspect the fleet. Upon hearing her godson was present aboard "Princess Royal", she requested his presence. That evening the fleet set sail to take part in the Baltic campaign. The ship engaged Russian forts at Hangö, before sailing to anchor at Køge Bay. In August 1854, Montagu saw action in the Anglo-French victory at the Battle of Bomarsund. Shortly thereafter the fleet sailed for Reval, where it lay anchor. In October 1854, owing to ill health, Lord Paget transferred Montagu to his old ship, . The ship returned Montagu to England, where he was collected by his father and taken to Ryde to recuperate.