The Buckfast Dadant was used from the 1920's by Brother Adam at Buckfast Abbey as a larger version of the Dadant hive, but with several modifications "to facilitate rapid and comfortable operation, and to simplify transport to the moors".
The supers were 6 in (152 mm) deep, which is half the depth of the brood boxes. It was also known as the "Buckfast Abbey Hive" and was available commercially. There is an advertisement in the seventh edition (1944) of W Herrod-Hempsall's "The Bee-Keeper's Guide" by Burgess & Son of 10 Goldsmith Street, Exeter. In it they state they are manufacturers of various items of equipment including the "Buckfast Abbey Hive".
The hive is 20" square, so has the benefits of being used "warm" or "cold" way. There are 12 Dadant frames, rather than the normal 11. This was to accommodate the huge colonies produced by the very prolific queens Br Adam preferred. The hive, rather strangely in my view, is bottom bee space. The roof has two sloping top parts in a similar fashion to a WBC roof to allow water to drain off quickly, but with flat end boards to retain a flat area. This was useful to rest parts on from adjacent hives, that were placed on stands in clusters of four at 90° to each other, each facing a different direction.
I have attended the West Sussex BKA auction every year for over 40 years and been the auctioneer for over 20, as well as travelling widely. I have only ever seen one Buckfast Abbey hive outside the abbey ownership. That was in a display of old equipment and I believe it may have originally belonged to Buckfast Abbey because of the distinctive colour. I suspect there weren't many sold, but I don't know.
More information will be added when available. If anyone has information or photographs, please email them to me.