However, on 11 December 1974 a Memorandum of Understanding was signed between the Federal Republic of Germany and the US about the common future production of a main battle tank; this made any application of Chobham armour dependent on the eventual choice for a tank type. Earlier in 1974 the Americans had asked the Germans to redesign the existing Leopard 2 prototypes, considered by them too lightly armoured, and had suggested adoption of "Burlington" for this purpose, of which type the Germans had already been informed in March 1970; the Germans however in response in 1974 initiated a new armour development programme of their own. Having already designed a system that in their opinion offered satisfactory protection against shaped charges, consisting of multiple-laminate spaced armour with the spaces filled with ceramic polystyrene foam as fitted to the Leopard 1A3, they put a clear emphasis on improving KE-penetrator protection, reworking the system into a perforated metal module armour. A version with added Burlington was considered, including ceramic inserts in the various spaces, but rejected as it would push vehicle weight well over sixty metric tonnes, a weight then seen as prohibitive by both armies. The US Army in the summer of 1974 faced the choice between the German system and their own Burlington, a decision made more difficult by the fact that Burlington offered, compared with steel armour, no weight advantage against KE-penetrators: the total armour system would have a RHA equivalence against them of about 350 mm (compared to about 700 mm against shaped charges). No consensus developing, General Creighton Abrams himself decided the issue in favour of Burlington. Eventually each army procured its own national tank design, the project of a common tank failing in 1976. In February 1978 the first tanks protected by Burlington left the factory when the first of eleven pilot M1 tanks were delivered by Chrysler Corporation to the US Army.