Most powerful steam locomotive

The worlds most powerful steam locomotive, measured by tractive effort, was No. 700, a triple-articulated or triplex six-cylinder 2–8–8–8–4 tank engine built by the Baldwin Locomotive Works in 1916 for the Virginian Railway, USA. It had a tractive force of 75,433kg 166,300lb when working compound and 90,519kg 199,560lb when working simple. No. 700's six cylinders each measured 864 x 813mm (34 x 32in). Its coupled wheels were 1422mm (4ft 8in) in diameter, grate area was 10.052m² (108.2ft²), total heating surface was 754m² (8120ft²), and its total weight was a massive 383 tonnes (377 tons). Unfortunately the engine was under-boilered and quickly ran short of steam. As a result, in 1921, the engine was divided, the rear being rebuilt into a 2-8-2 tender engine, and the front end into a 2-8-8-0 Mallet, No. 610 (a Mallet is a patented articulated locomotive design named after its inventor, Anatole Mallet). This was later rebuilt into a 2-8-8-2 and was withdrawn from service in the early 1950s. It was the only Mallet to have existed in three-wheel arrangements.
Note on tractive effort: Tractive effort is the force exerted at the rim of the driving wheel, measured in terms so the weight this force could lift vertically. The use the engine can make of it depends entirely on its ability to grip the rails, or its adhesive weight, and the capacity of the boiler to supply the steam.