Promoted to lieutenant, after first classes in every subject and maximum seniority, on 14 February 1889,[8] Brock joined the battleship HMS Trafalgar, flagship of the Second-in-Command of the Mediterranean Fleet, in April 1890.[7] After attending the gunnery school HMS Excellent, he became gunnery officer in the turret shipHMS Devastation at Devonport in August 1894.[7] He went on to be gunnery officer in the cruiserHMS Cambrian in the Mediterranean Fleet in October 1894 and gunnery officer in the battleship HMS Ramillies, flagship of the Commander-in-Chief of the Mediterranean Fleet, in November 1895.[7] Promoted to commander on 1 January 1900,[9] he became executive officer in the battleship HMS Repulse in the Channel Squadron in January 1901 and executive officer in the battleship HMS Renown, flagship of the Commander-in-Chief of the Mediterranean Fleet, in August 1901.[7] In July 1902 it was announced that he was appointed to HMS Albion, second flagship of the China Station,[10] but the appointment was cancelled the following week.[11] He was briefly posted to HMS Empress of India, serving in the Home Fleet, in early November 1902,[12] but in January 1903 he became commanding officer of the despatch vessel HMS Alacrity, serving on the China station.[13]
Promoted to captain on 1 January 1904,[14] Brock left the Alacrity after a year in January 1904, and became commanding officer of the newly commissioned Admiralty yachtHMS Enchantress in May 1904. He subsequently became Flag Captain to the Commander-in-Chief of the Mediterranean Fleet in the battleship HMS Bulwark in May 1905.[7] He went on to be assistant director of Naval Intelligence at the Admiralty in 1906 and then became Flag Captain to the Vice-Admiral commanding the Second Division of the Home Fleet in the battleship HMS King Edward VII in March 1909, before returning to the Admiralty as assistant director of Naval Mobilisation in August 1910.[7] After that he became commanding officer of the battlecruiserHMS Princess Royal in August 1912.[7] He was appointed an aide-de-camp to the King on 24 October 1913.[15]