When he arrived he found that there was an acute shortage of heavy express passenger and freight locomotives, which he met by developing a stock of capable, reliable and efficient engines. Over 2,000 were built in the period 1932-47, combining many features of GWR practice, such as tapered boilers, with LMS features such as outside Walschaerts valve gear which improved accessibility. His early boiler designs, with low-degree superheat and other Swindon characteristics, were unsatisfactory, for which he quickly rectified by revising the design with larger superheaters.

Locomotive design innovations included:

• 843 Class 5 4-6-0 mixed traffic 'Black Five" locomotives.
  
• 852 Class 8F 2-8-0 locomotives, consideral numbers being built by other railway companies for World War II service.
  
• His Princess Royal class of 1933 introduced the 4-6-2 express Pacific type to the LMS almost ten years after Hughes and Fowler had first proposed it.
  
• The Coronation class introduced in 1937, an enlargement of the Princess class, was one of the most powerful locomotives ever to run in Britain.
  
• Introduction of 0-4-4 tanks in 1932, 2-6-2 tanks and 2-6-4 tanks in 1935, 2-6-4 three cylinder tanks for the London Tilbury & Southend line in 1934, 2-6-0 'Lobster' freight engines in 1933.
  
• The Jubilee 4-6-0 mixed traffic engines introduced in 1934, were a development of the Patriot class, of which some were rebuilt by Stanier with taper boilers.
  
• Rebuilding of Fowler's Royal Scot class 4-6-0s, built 1927-30, with taper boilers and other changes.
  
• Introduction of 90 diesel-electric heavy shunting locomotives, including the type standardised by British railways.
  
• A prototype three coach articulated diesel-hydraulic train in 1938.