These locomotives were originally built by General Electric in the US as their model U8B (not by General Motors as stated in Tim Doling's book) and were supplied to the then southern system in the early 1960's. Building commenced in 1963 (again not in 1960 as stated in Tim Doling's book). The 'handshake' logo on the cabs of the BB's suggests some sort of donation? Apparently they were purchased (along with 200 "20 ton and 30 ton" freight wagons) using part of a US$7.8 million grant from the US. They were originally classified as BB907 class and were numbered 907 to 954. After 1975 they became part of the new unified rail system and were re-classified as D9E class, numbered from 207 to 254*. They have Caterpillar D398 12 cylinder engines rated at 900 hp/678 kw. They appear to be  a pretty rugged and reliable machine as quite a few are still in operation nearly 50 years after delivery. These machines seem to operate mainly in the south of the country, around Sài Gòn. An attempt has been made to re-engine several with new Caterpillar engines giving a slight increase in power. The modified machines are classified as D10E class, but the road numbers appear to stay the same.No furher locomotives have been converted.

Similar locomotives are/were in operation in a number of countries including New Zealand and The Philippines.

* I originally assumed that these locomotives were numbered from 201 but have since discovered that they are actually numbered from 207. I have a photo of  D9E-254 but no photos of any locos before 207 so it makes sense.

Steam Locomotives generally used the traditional French classification system. A steam locomotive with a 2-8-2 wheel arrangement is classified as 141 class, a locomotive with  4-6-2 wheel arrangement is classified as 231 class etc. To differentiate between different locomotives with the same wheel arrangement, the initial road number was added, e.g. 231-400 and 231-500. Some northern locomotives of Chinese origin were also known by their Chinese classification. e.g. 141 also known as ZL.

Diesel locomotives have a completely dfferent clasification system.

All diesel classes start with the letter 'D'  (for diesel or possibly dau may for engine?) then a number which I believe is related to the locomotives  power output. The third character defines  Electric' (E) or hydraulic  (H).

e.g. D5H class = Diesel + 500 hp + hydraulic.

Before 1975 in the south  diesels used the French system , e.g. BB for  Bo-Bo type locomotive then the initial road number. e.g. BB901 class.

In the North there appears to have been a mixture of different systems.

There is also a semi-official system where locomotives are classified by their country of origin. e.g D5H is also known as 'Ừc' (Australian).