The problems which beset the units following their introduction have been well documented, they followed the explosion at Renton on December 13th 1960 and a second less than a week later at Easterhouse.  On 19th  December the electric units were withdrawn and steam locomotives and stock hurriedly assembled to provide an emergency replacement service.  The completed motor coaches were sent to the Great Central workshops at Dukinfield in Manchester for modification, with those still under construction received the modifications before being released from Pressed Steel.  Further trials were carried out on the Styal line during March 1961 and in the Glasgow area from May that year.  Full services were re-introduced on October 1st 1961.
By the mid 1960s the 303s were considered Britain's most complicated electric units. Since their return to traffic, modifications and changes in the quest for higher component reliability and longevity had ran into hundreds, including the strengthening of the floor in the vestibules to combat the effects of stiletto heels.  Investigations continued towards a reduction in down time, as at that time there was a diagramming provision for 19 units to be continually out of use for maintenance. Can you imagine 79% availability being considered acceptable today! 
Initial major modifications included unit No.071 being fitted with silicon rectifiers and eventually all mercury arc rectifiers were gradually replaced with silicon rectifiers, but of smaller dimensions than the fitment in No. 071.  Unit No.091 was originally earmarked  to be fitted with thyristor equipment eventually fitted to 035.  The type of sliding doors with which unit No.035 was uniquely fitted (hence its Type AM3/2 classification) was originally to be applied to 50 or 60 units, but the plan was abandoned because of manufacturing difficulties. These air-operated doors were flush with the coach body when closed, and when opened moved outward and slid along the coach exterior; in service the equipment suffered a failure rate 150 per cent worse than that of the standard door gear on the other units.

In 1967 the electrification was extended to Gourock and Weymss Bay via Paisley and it was decided that a further 19 units were required.  Unfortunately in the intervening six years Pressed Steel had ceased trading and the order was placed with the Cravens Company of Sheffield.  These units were designated Class AM11 (later 311) and were structurally almost identical to the Class 303 sets.  The first of the new batch was delivered in July 1966 and featured fluorescent lighting and the bogie frames, still using the Gresley double-bolster design, were reinforced in an attempt to prevent the cracking that had appeared on some of the existing units. The traction motors were air-cooled from ducts positioned well above rail level to avoid the ingress of brake dust into the motors. The 311s could be easily discerned from the 303s by these additional bodyside vents on the Motor cars.  In view of the steep gradients on the new routes, particularly the Weymss Bay Branch, 222hp Metropolitan Vickers traction motors were fitted in place of the original 207hp motors fitted to the 303s.   Both classes also had their manufacturers name cast into the metal strip at each entry door.

All 303 and 311s were equipped to work at both 25kV and 6.25KV, as sections of power supply between Parkhead and Finnieston and near Dalmiur Park on the North Clyde, and round the Cathcart Circle were energised at this reduced voltage, due to the restricted clearances through tunnels and bridges.  Sections supplied at the lower voltage could be identified by the much smaller insulators on the overhead line equipment.  As part of the preparations for the West Coast Main Line Electrification and a result of increased experience of the insulation gaps required for overhead power supply technology, the Western side of the Cathcart Circle was converted to 25kV in 1973.   This allowed test running of WCML electric locomotives through to Shields Road depot while the paved track required in Eglinton Street tunnel was being completed.  By 1981, the remaining sections of 6.25kV were converted to 25kV and as a result electric locomotives could and did very occasionally appear under North bank wires, usually on Royal Train duties

The service scope of the class 303s was extended several times during their operational life.  Initial North Bank services between Airdrie, Springburn and Bridgeton to Milngavie, Balloch and Helensburgh were soon augmented with services from Glasgow Central to Motherwell and Neilston and round the Cathcart Circle.  Gourock and Weymss Bay followed in 1967 with the Hamilton Circle and Lanark services in 1974.  The North Bank services were isolated from the rest of the electrified network until 1979 when the Clyderail project linked Rutherglen with Finnieston Junction, allowing through services from Dalmuir to Hamilton and Milgavie with Lanark.  In August 1987 electric trains were introduced over the Motherwell to Coatbridge Central line, making use of the overhead equipment installed for freightliner traffic to Coatbridge. 1989 saw  further extensions in the Monklands area, with services being restored to Drumgelloch and the link between Sunnyside Junction and Whifflet being electrified as a diversionary route while the infamous Newton rationalisation project was in progress.  Some minor losses have been incurred, with the closure of the pier stations at Craigendoran and Balloch and the abandonment of the Bridgeton branch.

Livery Notes

The "Blue Train" nickname was a direct result of the decision to paint the units in Caledonian Blue, with standard passenger stock lining of yellow and black and the BR coaching stock crest applied to the Motor Brake Second only.  Unit numbers were not initially applied, the earliest example I have seen with the unit number applied on delivery was 015.   Minor changes to the livery in early years concerned the addition of small yellow warning panels below the cab windows. This followed a trial period when various shades and patterns of warning panel were applied.  Once the standard BR rail blue was chosen for all stock the 303s lost their distinctive livery, and the later class 311s were delivered from new in this livery.  The yellow warning panel was replaced by all over yellow for the cabs (initially including the driver's doors).   By the early 1970s the all over blue was relieved by the blue/grey coaching stock livery, and with the forming of Greater Glasgow (later Strathclyde) passenger transport executive the interleaved GG was applied to one trailer car in each set.
Major refurbishment of selected 303s commenced in 1986 which saw the adoption of the Orange (officially Strathclyde Red) and Black livery.  Initially the refurbishment was restricted to the décor and seating and sadly resulted in the end of the forward view through the drivers cab window.  Later alterations, retro fitted to units already refurbished included the fitting of internal gangways to aid the work of conductors following de-manning of stations, and the fitting of droplight windows.  The Strathclyde Carmine and cream livery was only applied to four sets.  Two units 303001 and 303048 were repainted into Caledonian Blue.  303001 was repainted in August 1985 to mark the 25th anniversary of the introduction of electric train services, and remained in this livery unitil the following year when it was refurbished.  303048, the last unrefurbished unit in service was repainted in March 1991as a celebrity charter unit (and route learner).  It had been intended to preserve at least part of this unit but the discovery of asbestos let to its scrapping in 1998.

Away from Glasgow

Once the units sent south for modifications returned north, the 303s became isolated in the Glasgow area, and there are no reports of them venturing away from their normal haunts from 1961 until the wires were erected on the West Coast Main line in 1974.  Twelve units were used to check the overhead electrical supplies on Beattock bank as part of the preparation for the introduction of electric services in early 1974. 
The increasing availability of units and a general reduction in timetable frequency led to a surplus of units in the Glasgow area in the early 1980s.  This permitted the reallocation of several Class 303s sets to the London Midland Region from 1981 onwards.  This was initially to provide cover for class 310s which were experiencing braking problems then  to replace elderly class 504 EMUs on the Manchester to Glossop and Hadfield services when these routes were converted to 25kV AC.  Initially allocated to Crewe Electric Depot, then to Longsight depot from 1985, the units could be found on various routes including the Manchester to Crewe line where they were tested back in 1960/61.  It was also not unknown for class 303s to work class 1 duties on the West Coast Main Line and both 303048 and 303066 are recorded as having worked Crewe - Carlisle relief services in 1984 and 1985.  From December 1984 onwards these units were painted in Greater Manchester PTE orange and brown (very similar to the Strathclyde colours), but it wasn't long before the units became unreliable and most units had been withdrawn or stored by May 1990.  303066 and 303049 even had the the dubious distinction of visiting North Wales, being stored at Llandudno Junction Shed in 1990.  Only three units returned north, the celebrity 303048 in July 1989 and 303060/082 following a period of storage in May 1992, neither of the latter two units return to service, and languished at  Yoker and Shields Road depots.  One of these two units was hauled to Leith Yard in 1993 or 4 for use as a mobile Rail Safety exhibition aimed at young people in Edinburgh.  Class 303s and 311s were also to be seen at Edinburgh on Driver training duties in preparation for the introduction of electric services on the North Berwick branch

303 Sub classifications
303/1 - Original unmodified units 
303/2 - Fitted with Dean doorgear until 1971(303035)
303/3 - Fitted with silicon rectifiers and oil cooled fans (303071)
303/4 - Thyristor control, oil cooled rectifiers (303035 from 1971 - 1981)
303/5 - Fitted with silicon rectifiers with oil cooling of transformer and rectifier 
303/6 - Fitted with silicon rectifiers with separate oil cooling 
303/7 - Fitted with air cooled silicon rectifiers
 

Unit Formation History:- Units 303001 to 303031

Unit Formation History:- Units 303032 to 303061

Unit Formation History:- Units 303062 to 303091

Unit Formation History:- Units 311092 to 311110