[9] Rainier was educated at private schools before entering HMS Britannia in December 1860 as a cadet, scoring first of thirty-four successful candidates.

[1][3] Appointed to the command of the composite screw sloop HMS Kingfisher for service on the East Indies Station in 1884,[11] Rainier landed at Zeyla in February 1885 with seamen and Royal Marines to assist in the arrest of mutinous Somali police.

[3] The same year, whilst in command of the Kingfisher, he was a member of the Defence Committee of Mauritius, and received the thanks of the Governor.

[3][11] Promoted to captain in 1887,[12] Rainier was next appointed to the command of the corvette HMS Tourmaline in 1889 on the North America and West Indies Station.

[13] In February 1897, Rodney joined the International Squadron off the coast of Crete during the island's revolt against Ottoman rule.

[14] In March, following reports of massacres of Muslims by Christian insurgents, Rainier led an international landing force consisting of 200 British Royal Marines and sailors, 100 men each from Austro-Hungarian and French warships, 75 Russians, and 50 Italian sailors on an expedition inland to Kandanos (also spelt Candanos), which rescued 1,570 Muslim civilians and 340 Ottoman soldiers from Kandanos and 112 Ottoman troops from a fort at Spaniakos (or 3,000 in total according to some contemporaneous sources) and evacuated them by sea.

For his part in the expedition, Rainier was mentioned in despatches and personally thanked by the senior foreign admiral.