MP4 is the initial for Mclaren Project 4, not Marlboro Project 4 like Fuzzy mentioned above. Marlboro only played role in merging Mclaren's team with Ron's new Project 4 outfit, back in the early 80's.
Until 1980, Ron was running March chassis in F3 and F2 under the Project 4 banner. Plans to enter F1 in the early seventies had been abandoned (Muks_C is right about Ron had three less succesful of failed companies/project/attempt before the fourth one which is Project 4) and he felt the time was then right for another attempt. He wanted to do it properly, and sought out an ambitious young designer called John Barnard who was making his name in the US.
The collaboration between Ron and John resulted Project 4's success, which is the first F1 car with a carbonfibre chassis. Ron wanted a chassis of smaller section, and retain the stiffness. So the only way is, to change the material (John suggested). Ron was brave enough to agree to the plan, despite the obvious risk it placed on his fledgling set-up.
Ron had been hard at work behind the scenes, and it paid off. In September 1980 it was revealed that Marlboro had arranged a merger between Ron's new Project 4 outfit and the Mclaren team. The MP4 chassis was formed from five major components, and consisted of mostly flat panels; the technology to make curved pieces would come later. The prototype had an aluminium front bulkhead, but otherwise was entirely made from the new material. It was launched on March 5 1981, and John Watson and Andrea de Cesaris had to use the old M29 at the start of the season, before they got hold of the MP4 for the third race in Argentina.
Now, think back...why would Mclaren do such thing, like throwing away it's own initials to give way for sponsors? 100% nay as Mclaren is a privateer back then and everyone knows that privateers seldom change their chassis/car name to please their sponsors. The M was never the initial of Marlboro, despite being sponsored heavily by the tobacco giant company back in the 80's and early 90's.
So clearly, MP4 stands for MCLAREN PROJECT 4, not MARLBORO PROJECT 4 (this never exist).
Post Edited (04-04-04 11:21)