He subsequently designed an articulated compound system with a rigid chassis at the rear carrying two high-pressure cylinders, and two low-pressure ones mounted on a swivelling front truck. This was patented in 1884 with full rights granted in 1885. This was first used for a series of narrow gauge locomotives specially built by the Decauville Company in 1888 for the Paris Exposition of 1889. This arrangement became known as the Mallet locomotive. The final developments of these in the USA were some of the largest steam locomotives ever built.