"When Bomber Command became Strike Command there was no delay in creation of a new crest" - a new badge can be created based on one that has previously been approved for a unit with a similar role. Such badges are known as "close copies".
12 Sqn's motto "Leads the field" not only reflects the chasing of foxes, but also the fact that the Fairey Fox - a bomber - was apparently faster than the fighters in service at the time!