The Cholas maintained a strong navy and the contribution of the naval forces were important in the Chola conquests of Ceylon(Sri Lanka), the Arakan coast of Burma(Myanmar), Malay Peninsula, Islands of Sumatra, Java, Borneo (then Sri Vijaya and and present day Indonesia).
The Chola navy had around 1000 ships and a million sailors. The Chola navy had a complex classification of classes of vessels and their utility. Dharani was equivalent of modern day destroyers designed to take combat to high seas. Loola was the equivalent of modern day corvettes, designed to perform light combat and escort duties. Vajra was equivalent of modern frigates, fast attack, lightly armoured crafts. Thirisadai was equivalent to modern battle cruisers or battleships. They had extensive warfighting capabilities and endurance with a dedicated marine force of around 400 marines to board enemy vessels. There were also large vessels called Kalam, large barge type vessels called Patri, medium type boats called Ambi, small boats called Oodam and small boats for rocky terrains called Toni.There were also royal yachts called Akramandham, Neelamandham, Sarpamugam etc.
The Emperor was the Supreme Commander. The Commander-in-Chief of the Navy(Kadalpadai) was called Jaladhipathi, equivalent to the modern day Admiral of the Navy.The Navy had many fleets called Pirivu. The Fleet was commanded by Pirivu Adhipathi, equivalent to the modern day Admiral. Below the Fleet was the Fleet Division called Ani, composed of 300-500 ships. It was commanded by an Anipathi, equivalent to a Vice Admiral. An Ani was formed by three ganams. A Ganam had 100-150 ships in it and was commanded by a Ganathipathi equivalent to a Rear Admiral. A Ganam was composed of three Mandalams. A Mandalam had about 50 ships and was commanded by a Mandaladhipathi, equivalent to modern day Commodore. The smallest self sufficient unit was called Jalathalam, commanded by a Jalathalathipathi with around 15 ships. The officer who commanded a ship was called Kalapathi, equal to the modern day Captain in the Navy. There were other junior officers called Kaapu, Seevai, Eeitimaar etc.
Besides the standing navy, the Customs Department had their own naval force called Sungu. There were also State agencies like Thirvai(Customs and Excise), Aaivu(Inspection and Enforcement), Ottru(Intelligence Corps) etc. As the Navy was more engaged in far away lands, a separate Coast Guard called Karaipirivu was formed to protect the territorial waters, home ports and coastal cities.