Harold Holcroft

Harold Holcroft (12 February 1882 – 15 February 1973) was a British railway and mechanical engineer who worked for the Great Western Railway (GWR), the South Eastern and Chatham Railway (SECR) and the Southern Railway (SR). At the GWR, Holcroft helped the Chief Mechanical Engineer (CME), George Jackson Churchward, design the 4300 class 2-6-0 Moguls, and took the design principles for this class of locomotive with him when he moved to the SECR. Here, he worked as Assistant to Richard Maunsell and was involved with the design of the Maunsell Moguls, transferring to the Southern Railway when it was created by the amalgamation of the SECR with other railways at Grouping in 1923. After Maunsell's retirement in 1937, Holcroft continued to work for the Southern Railway under Oliver Bulleid until his retirement in 1946.

Holcroft was born at Wolverhampton in 1882 and undertook a premium apprenticeship at the Wolverhampton works of the GWR (managed by his uncle Ernest Edward Lucy). He worked in the assembly shop and the drawing office to get an all-round feel for railway life, giving him the experience to generate his own ideas. His first patent was filed at the age of 18, which brought Holcroft to the attention of Churchward and enabled him to transfer to Swindon works when his apprenticeship was completed. As one of Churchward's rising prodigies in the heyday of GWR locomotive development, Holcroft helped with the design of several of Churchward's locomotives, notably the 4300 class 2-6-0. In 1909, he patented a form of conjugated valve gear to drive the valves of a three-cylinder engine from only two sets of valve gear.

When the Churchward development programme of new locomotives began to slow down, Holcroft sought employment with a railway still in need of original design work. He joined Richard Maunsell's design team as an Assistant, participating in the latter's contributions to the SECR and Southern Railway's motive power.

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