A whaler or whaling ship is a specialized ship, designed, or adapted, for whaling: the catching or processing of whales. The former includes the whale catcher – a steam or diesel-driven vessel with a harpoon gun mounted at its bow. The latter includes such vessels as the sail or steam-driven whaleship of the 16th to early 20th centuries and the floating factory or factory ship of the modern era. There have also been vessels which combined the two activities, such as the bottlenose whalers of the late 19th and early 20th century, and catcher/factory ships of the modern era.
Whaleships had two or more whaleboats, open rowing boats used in the capture of whales. Whaleboats brought the captured whales to the whaleships to be flensed or cut up. Here the blubber was rendered into oil using two or three try-pots set in a brick furnace called the tryworks.
At first, whale catchers either brought the whales they killed to a whaling station, or factory ship anchored in a sheltered bay or inlet. With the later development of the slipway at the ship's stern, whale catchers were able to transfer their catch to factory ships operating in the open sea.
The World War II Flower-class corvettes were based on the design of the whale catcher Southern Pride.[en]