The T3 tanker, or T3, are a class of seaworthy large tanker ships produced in the United States and used to transport fuel oil, gasoline or diesel before and during World War II, the Korean War and the Vietnam War. The T3 tanker classification is still used today. The T3 tanker has a full load displacement of about 24,830 tons.

A tanker is a ship designed to transport or store liquids or gases in bulk. Major types of tankship include the oil tanker, the chemical tanker, cargo ships, and a gas carrier. Tankers also carry commodities such as vegetable oils, molasses and wine. In the United States Navy and Military Sealift Command, a tanker used to refuel other ships is called an oiler but many other navies use the terms tanker and replenishment tanker. Tankers were first developed in the late 19th century as iron and steel hulls and pumping systems were developed. As of 2005, there were just over 4,000 tankers and supertankers 10,000 LT DWT or greater operating worldwide.