Rectangular tank wagons were some of the earliest dedicated designs for carrying liquids by rail and date from the mid-1800's. Previously barrels of liquids had been transported in open wagons, but these didn't fare well in the many accidents suffered by the early railways.

Although all kinds of liquids were initially carried, volatile spirits were banned from these wagons in 1902. One of the downsides of the box shape was that as the contents sloshed around, vapours could be trapped and compressed in the upper corners of the tank, leading to explosions. Having a low centre of gravity however, the tanks were well suited to dense liquids such as tar.

Until the late 1960s most homes in the UK received "town gas", a mixture of flammable gases produced locally in "gas works" by heating coal in the absence of oxygen. The by-products included coke, used in steel production and tar, used to produce a wide range of products including coal-tar soap, benzole petrol and pharmaceuticals. Gas works would ship tar by rail, meaning many rectangular tanks remained in service until natural gas was adopted across the UK between 1967 and 1977.

Basically a steel box on a conventional wagon chassis, these wagons differed in how the tank was secured and by variations in filling/emptying fittings.

Two examples are included, based on one produced in 1877 now kept at the Scottish Railway Preservation Society, Bo'ness and a second dating from 1898 based at the Great Western Society, Didcot.

Other examples of these wagons can be viewed on Paul Bartlett's Wagon site: https://paulbartlett.zenfolio.com/?q=rectangular

Both bodies are intended to fit the Peco NR-119 9' Wooden-type chassis kits.

Some suitable decals are available from Robbie's Rolling Stock: http://www.robbiesrollingstock.co.uk/Tank_Wagons.htm