Given the strained government defence budget in the early 1930s, due to the effects of the Great Depression, the acquisition had to be split up in batches: the first 18 units were ordered on 10 March 1934, and delivered in two lots of nine on 15 and 22 February 1935. The second batch of 24 units was ordered on 16 April 1935 and they were delivered between 15 November – 28 December 1935.
