With hostilities on the horizon, France went to North American for a version of the BT-9 called the NA-57. these proved very popular, so, just before the war, they ordered a further 230 updated machines. This incarnation was called the NA-64, later to be called the YALE I.

It was a hodge-podge machine, featuring the Harvard canopy, the fixed landing gear and the Wright Whirlwind engine. It did, however, have the semi-monocoque rear fuselage rather than the earlier fabric structure. It retained an early wing type, which gave it certain vicious stall characteristics. Later modifications to correct this were never really successful so the aircraft kept its reputation of biting the unwary.

One hundred and eleven of these had just been delivered when France fell. The Germans were happy to press them into service in the Luftwaffe, many still in their packing crates, as they too had a shortage of trainers.

The one hundred and nineteen remaining aircraft were drafted by the RCAF. They arrived in Canada in their packing crates, complete with French markings, instruments and control linkages. They were, more or less, Canadianized at National Steel Car and went on to serve as intermediate trainers, with the HARVARDS then being considered advanced trainers. They were withdrawn from service in 1943 as this extra stage was deemed unnecessary. Some of them, however went on to become wireless trainers.

Many,if not all, of the Yales still flying today came from the collection of the late eccentric Ernie Simmons, of Tillsonburg, Ontario.