Underway replenishment oiler

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The USNS Big Horn (T-AO-198), an underway replenishment oiler.
The USNS Big Horn (T-AO-198), an underway replenishment oiler.

The underway replenishment oiler is a type of ship of the United States Navy. These oilers provide underway replenishment of fuel to U.S. Navy ships at sea and jet fuel for aircraft assigned to aircraft carriers. In the British Royal Fleet Auxiliary (naval auxiliary service), such vessels are known as Fleet Tankers.

Features: There are stations on both sides of each ship for underway replenishment of fuel and stores.

Background: Fitted with medium-speed diesel propulsion, the delivery of USNS Patuxent (T-AO-201), Rappahannock (T-AO-204) and Laramie (T-AO-203) was delayed by the decision to fit double hulls to meet the requirements of the Oil Pollution Act of 1990. This modification increased construction time from 32 to 42 months and reduced cargo capacity by 17 percent, although this can be restored in an emergency. Hull separation is 6 ft (1.8 m) at the sides and 6½ ft (2.0 m) on the bottom.