Beginning in the 1840s, the normal entry age for executive officer cadets, those destined to command ships and fleets, was between 12 and 13, and instruction consisted of two years of classroom training, during which time trainees were rated as naval cadets. Cadets who received a first-class passing grade in studies, seamanship and conduct on their final examination could receive a credit for up to a year of sea time, and could be rated as midshipmen immediately after passing out of the college. After passing out of the college, cadets served aboard a special training vessel for one year. Cadets were then rated as midshipmen, and served aboard the fleet another two years. Midshipmen lived in the gunroom, kept watches, and ran the ship's boats. They received instruction in navigation every day. After five total years of training and having reached the age of 19, the midshipmen were eligible to take the examination for lieutenant. After passing the examination for lieutenant, midshipmen were commissioned as sub-lieutenants, and were transferred to the Royal Naval College, Greenwich, which opened in 1873 as the 'University of the Navy'.