With hindsight the Sabre fiasco seems like a mistake.
However, when the decision was taken to proceed with its development there was more at stake than the promise of the engine itself.
The Air Ministry always believed that quality could only be assured by competition between the different firms and the rapid contraction of the aero engine industry during the 1930s was the cause of much concern. As early as 1st July 1935 Sir Christopher Bullock, Permanent Under-Secretary at the British Air Ministry, was writing that it was,
"essential that Messrs. Napiers should be kept alive as a separate entity, in order to prevent the engine industry being constituted on too restricted a basis."
In February 1937 Freeman was alarmed that,
"the loss of the experienced personnel making up the technical division [of Napier] would be a serious loss to the RAF."
It got worse. By May 1939 he was expressing his concern that both Napier and Armstrong Siddeley were on the verge of leaving the aero engine business altogether.
"It was a most unhealthy position" he wrote "for the Air Ministry to be substantially dependent upon two firms only."
The development order for six Sabres was placed in 1937, coinciding with plans for a new Sabre engined fighter to replace the Spitfire and Hurricane (eventually the Typhoon). There were on going problems with the development of the next generation engines from the other two firms. The R-R Vulture suffered repeated failures during 1939. The Bristol Centaurus was still a very long way from being a production engine, and the production arrangements for the Hercules had been pushed through by the Air Ministry before it was certain that it would be a successful engine.
The decision to gamble on the Sabre was based on two factors. First, the Sabre would provide a third option should the Vuture and Centaurus fail. Second, It would keep Napier in the aero engine business, something that was considered essential by the Air Ministry at the time. On this basis it doesn't seem quite the disastrous mistake that the Sabre would make it seem. Nobody could know in 1937 that the Sabre would turn into one of the most difficult and costly of all pre-war development projects.