After Pearl Harbor (Dec. 7, 1941), when it became a full belligerent, the United States and fourteen of its allies signed master lend-lease agreements providing for reciprocal aid and the pooling of human and material resources directed and coordinated toward the common goal. From that date forward the United States furnished nearly every kind of material and service to its allies, and received in return much the same kind of aid. Mindful of the World War I debt fiasco, as a result of American loans to its allies and the hard feelings that followed, the negotiators drafted Article VII of the master lend-lease agreements to provide that "the terms and conditions thereof shall be such as not to burden commerce between two countries but to promote mutually advantageous economic relations between them and the betterment of world-wide economic matters." The British provided numerous bases and supplies for American forces, and furthermore gave the Americans the Rolls Royce Merlin engine for the P-51 Mustang fighter, the blueprints for the proximity fuze, and vital information on the atomic bomb.