AEC's Blue Triangle symbol [© AEC Ltd] is reproduced by kind permission of The British Commercial Vehicle Museum Trust.
ALSA (La Sociedad Automóviles Luarca, S.A.) is now the main coach operator in Spain with international businesses reaching China, but in the Forties and Fifties ALSA was just a regional operator based in Luarca and Oviedo, in the Spanish northern region of Asturias.  Their flagship service was the 170km Oviedo-Luarca-Ribadeo line, with thirteen fixed and thirty occasional stops.
The ALSA fleet had been based mainly on NAG and Saurer vehicles, with some additional GMCs, Renaults and Hispano-Suizas. In 1939/40 they bought around seven A.C.L.O. normal control coaches.  In 1948 two of them, fleet numbers 53 and 54, received a double deck body by Seida of Bilbao.  Sometime around that year ALSA became an A.E.C. dealer for Spain and an office was opened in Madrid.  A.E.C.s were sold as A.C.L.O.s in Latin America including Brazil, and Spain, but not in Portugal.
In the early 1950s ALSA bought a batch of seven forward control, front engined, long wheelbase A.C.L.O. chassis (presumably Regal IIIs) which were also bodied by Seida.  They entered service in 1953/54 and received fleet numbers from 63 to 69.  A pair of similar chassis with the traditional A.E.C. exposed radiator came in 1955 and received a slightly different body; these were numbered 70 and 71.  By that time a new ALSA express fixedstop service between Oviedo and Ribadeo connected with the Ribadeo-Corunna line operated by Empresa Ribadeo, creating a full Oviedo-Corunna service, a distance of 320 kilometres covered in 12 hours.  Empresa Ribadeo operated Leyland Tiger coaches bodied by Barro of Chavin, the passengers switching between A.C.L.O./Seida and Leyland/Barro.
Around 1957 a pair of medium size front engined vehicles joined ALSA fleet, and eventually a few A.C.L.O. underfloor engined coaches (thought to be Regal IVs) were delivered in 1959/60.  The bodies were not by Seida this time; fleet numbers were in the 90s.  Alsa was mainly buying Pegaso chassis with Seida bodies, and this was so for the following fifteen years, until Mercedes-Benz chassis with Irizar bodies became the standard.
Interestingly the very last ALSA A.C.L.O. was actually an A.E.C.  In 1962 Barreiros Diesel and A.E.C. signed an agreement to build AEC coaches in Spain to be sold as "Barreiros A.E.C.s", and as a consequence Barreiros became the exclusive A.E.C. dealer for Spain  In February 1963 ALSA bought A.E.C. Regal Mk IV coach chassis U2LA585, with Barreiros acting as dealer.  Numbered 101 in the ALSA fleet, the chassis had a horizontal AH690 engine, number AH6906X84.
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Early normal control A.C.L.O. (98Kb)
Early normal control A.C.L.O. seen in Ribadeo circa 1948. The pipework around the roof belongs to the 'gasogeno' system used to feed the engine instead of fuel in the post-war era of fuel shortage. Normal control A.C.L.O. (74Kb) Another normal control A.C.L.O. seen at Vegadeo in 1960.
Normal control A.C.L.O. double decker (122Kb) This is one of the double-deck A.C.L.O.s pictured outside the Seida works just before delivery to ALSA. Normal control A.C.L.O. double decker (94Kb) An A.C.L.O. double-decker seen working the route from Oviedo to Ribadeo.
Forward Control A.C.L.O. (138Kb)
A new forward control A.C.L.O. taking a break during the trip from Seida works to ALSA headquarters most likely in 1953. The banner on the upper side advertises ALSA as A.C.L.O. dealer, while "Seida" (the bodybuilder) is displayed in the destination indicator. Forward Control A.C.L.O. (118Kb) One of the two forward control A.C.L.O.s with exposed radiators pictured circa 1959. Note the cheap third class seating on the roof, discontinued in 1960.
Pictures and text provided by Lino Lopez-Cotarelo

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(some dates published at this website are somewhat inaccurate)