The Birmingham and Midland Motor Omnibus Company Limited (BMMO—Midland “Red” Motor Services) reintroduced motor omnibuses on Saturday 25th May 1912, after initially abandoning them in October 1907 due to poor reliability. From that time until the early 1920s the BMMO fleet was populated almost exclusively with petrol-electric Tilling-Stevens vehicles but this type of design had quickly become obsolete after the First World War, following the introduction of more advanced designs from overseas, and BMMO looked to other manufactures to evaluate alternatives.
It would appear there were no suitable alternatives available readily on the British market so BMMO embarked on a program to build their own vehicles, a practice that would continue until 1970 with the only interruption being during the Second World War. Between the wars, vehicles built to BMMO design carried the name SOS† and the first design was known simply as the “Standard” SOS, although long after the class disappeared from the roads the unofficial abbreviation SOS “S” became commonplace.
† No official record has been found to confirm the meaning of the initials “SOS”, but two versions are commonly used. These are “Superior Omnibus Specification” and “Shire’s Own Specification”, the latter being suggested as being named after Mr LG Wyndham Shire, the Chief Engineer at BMMO from 1912 until his retirement in April 1940.
Three chassis were supplied to BMMO by Tilling-Stevens in the summer of 1923. These were based on the established Tilling-Stevens TS3 15′ 6″ wheelbase design but were custom built to BMMO specification with a number of enhancements and modification, and did not carry chassis numbers.
The most significant changes to the TS3 specification was the fitting of a conventional engine and gearbox transmission to replace the petrol-electric transmission, and the use of pneumatic tyres instead of the solid tyres previously used.
Two of these chassis (registration numbers HA2330 and HA2333) were fitted with B32F bus bodywork built by Brush, and the third (registration number HA2348) with Ch32 Davidson charabanc bodywork. These three vehicles were the prototypes for BMMO’s first bus design, the “Standard” SOS.
From late 1923 and throughout 1924, Tilling-Stevens supplied fifty-eight production “Standard” SOS chassis to BMMO, plus an additional twenty-three to other operators, with Potteries Electric Traction taking twelve, Peterborough Electric six examples, Llandudno Royal Blue four examples, and one to Northern General Transport.
Unlike the three prototypes these did carry chassis numbers, and were numbered from 3015 in-line with the general Tilling-Stevens production sequence at the time. Despite being called “Standard”, this batch were far from standardised as the specification constantly evolved as BMMO changed and improved their design, and gradually reduced the component parts sourced from Tilling-Stevens. For example, partway into production the radiator changing from have “Tilling-Stevens” cast into the tank top, to a new wider design with “Midland Red” lettering, and the front wheel hubs changed from standard small Tilling-Stevens items to larger ones with “SOS” inscribed on polished caps.
Three different engine types were also used on these vehicles, presumably to test which options would be best for future use. The first was the BMMO “Wonder” engine, which was originally developed in 1922 for use on the Tilling-Stevens FS, as a modified version of the standard Tilling-Stevens engine. In addition to these, BMMO’s own 4.3-litre “SOS” petrol engine, using cylinder heads designed by Harry Ricardo, was used in two versions. One version being built by Wolseley on behalf of BMMO, and the other built in-house by BMMO at their workshops at Bearwood depot.
These Tilling-Stevens built vehicles became known as “1924 Standard” and entered service fitted with either B32F bus bodywork by Brush (registration numbers HA2334–2347 and HA2359–2392) or Ch32 charabanc bodywork by Davidson (registration numbers HA 2349–2358).
Production of the “Standard” SOS chassis moved to BMMO’s own workshops located at Bearwood depot in 1925. The “Standard” SOS chassis built here became known as “1925 Standard” and were the first chassis to be fully construction by BMMO at their own workshops to their own design.
The first chassis built by BMMO (chassis number BMO.1) became registration number HA2393, and construction of the “Standard” SOS chassis continued into early 1926, by which time BMMO had built 271 examples. Of these, 120 were built by BMMO for their own use, while the remaining were built for other operators, such as Northern General Transport with sixty examples, Potteries Electric Traction with thirty-one and Trent Motor Traction with thirty-two.
There were a number of changes to the design of the “1925 Standard” built by BMMO, when compared to the earlier vehicles built by Tilling-Stevens. The most significant of these was the increasing of the wheelbase by 1½″ to 15′ 7½″, and reducing the overall chassis length from 24′ 0¾″ to 23′ 7½″. The engine was also standardised to a BMMO-built unit which would continue to be used on production vehicles until 1930.
Of the chassis built by BMMO for their own use, six were fitted with Ch32 charabanc bodywork by Davidson (registration numbers HA 2435–2440), while all others were fitted with B32F bus bodywork built either in-house by BMMO (“Carlyle”), or supplied by Brush or Ransomes, Sims and Jeffries.
One vehicle from this batch, registration number HA2500, was built with the chassis modified for forward control, having the driver’s controls alongside the engine and not in the normal position behind the engine. The bodywork fitted was built in-house by BMMO (“Carlyle”) to the same general design and style as the other “Standard” SOS buses, but suitably modified with an enclosed forward control driver’s cab over the offside front wheel. These modifications generated more space in the passenger saloon, allowing seating capacity to be increased from 32 to 34. This vehicle was still classified as “Standard” SOS, although it was regarded as a prototype for the SOS “FS” class.
In 1927, BMMO sold eleven of their “1925 Standard” buses to either Northern General Transport (registration number HA2435–2440) or Peterborough Electric Traction Company (registration numbers HA3501–3505), when only one or two years old, but these went on to see a useful amount of service with their new owners. One of these, registration number HA3501, survives to this day and now lives at the Transport Museum, Wythall (BaMMOT) although a major restoration will be required before it returns to the road.
The “1924 Standard” charabancs with Davidson bodywork, including the prototype, were all withdrawn in 1928 (registration numbers HA 2348–2358). These were all still relatively young vehicles as even the prototype was less than 5-years old, but clearly the company could see no further need for them once the SOS “QC” class had been introduced. One example, registration number HA2356, did see further service as a driver training vehicle until 1932.
Ignoring vehicles that were converted to SOS “ODD” (see below), the main bulk of withdrawals started in 1933 and by the end of the following year the entire class had gone.
The first “1925 Standard”, registration number HA2393, was withdrawn in 1929 and the bodywork removed. The chassis was then extensively refurbished, receiving new running units and smaller wheels to reduce height, and fitted with new B27F United Automobile bodywork, as the prototype SOS “ODD”. The conversion gave the vehicle a much more modern look and was clearly judged to be a success as in 1930 BMMO converted an additional fifty vehicles of their own (registration numbers HA2400–2434 and HA2441–2455), plus a number of examples being operated by other companies. The fifty vehicles converted in 1930 differed slightly from the 1929 prototype in that they had a B26F seating layout, and a slightly different window design.
The conversion extended the life of the BMMO examples by around four years, with the vast majority being withdrawn in 1938. Three examples saw further use as driver training vehicles until 1943 (registration numbers HA2443 and HA2450) and 1946 (registration number HA2442), while one example (registration number HA2453) survived as a tree cutter until 1952.
Details of these early vehicles are not easy to come by, so all of the information on this page has been sourced using various previously published works by John Seale, Paul Gray and Malcolm Keeley, and the Birmingham and Midland Motor Omnibus Trust (BaMMOT).