The T1 tanker or T1 are a class of sea worthy small tanker ships used to transport fuel oil before and during World War II, Korean War and Vietnam War. The T1 tanker classification is still in use today. T1 tankers are about 200 to 250 feet in length and are able to sustain a top speed of about 12 knots. The hull designation AO is used by the US Navy to denote the ship is a T1 oil tanker and AOG that the T1 is a gasoline tanker. The small size allows the T1 to enter just about any sea port or to anchor around a small island, this was very useful during the Pacific War. The T1 tanker can carry about 48,000 to 280,000 bbls. Some T1 tankers were used to transport goods other than oil, a few were used for black oil-crude oil, diesel, chemicals and rarely bulk cargo like grain. T1 tankers are also called liquid cargo carriers. The T1 tanker has about a 6,000 to 35,000 deadweight tonnage (DWT) of cargo. The small size also gives the ships short turn around time for repair, cleaning, loading and unloading. A T1 tanker carrying dirty cargo, like crude oil needs a few weeks of labor to clean before carrying clean cargo. Most T1 ships during World War II were named after major oil fields.

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.