The first product of the BL-Honda alliance was the Triumph Acclaim – and shortly after its launch the two companies mapped out an advisable strategy for future collaborative projects. Plans for a midsize car were investigated, but were dropped because BL already had the Austin Maestro and Austin Montego in the final stages of development. However both BL and Honda had a pressing need for a full-size executive car in their lineups. BL had to start planning for a successor to the Rover SD1, whilst Honda was keen to expand its presence in the lucrative North American market – something which it couldn't fully do unless it had a full-size luxury saloon (at that time the Honda Accord was its biggest model) which would compete with similar large Japanese imports from Toyota and Datsun. Joint development of the car began in 1981 under the "XX" codename; the corresponding Honda version was known as the Honda Legend, and was codenamed as "HX". The development work was carried out at Rover's Cowley plant and Honda's Tochigi development centre. Both cars shared the same core structure and floorpan, but they each had their own unique exterior bodywork and interior. Under the agreement, Honda would supply the V6 petrol engine, both automatic and manual transmissions and the chassis design, whilst BL would provide the 4-cylinder petrol engine and much of the electrical systems.