I am not sure when it began, but in the sixties and early to mid seventies the London Fire Department used a very different numbering system for the rigs.

All pumps were numbered in  a 10 series, eg. Unit 11 was the pump from Station 1, Unit 12 the pump from Station 2 and up to eventually Unit 19. The aerials were a 20 series.Unit 21 the aerial from Station 1, Unit 22 from Station 2 and Unit 28 from Station 8. The rescue was Unit 8 and the tanker was Unit 9. The service/brush truck was Unit 54. Unit 1 was the Department Chief, Unit 2 was the Deputy Chief, Unit 3 was the Platoon Chief and Unit 4 was the District Chief. Today London uses the Engine and Truck designations in numerical order.

London still stays somewhat unique as most Ontario departments use the designation of pump and aerial or ladder