文件:Los Alamos Primer assembly methods.png

It depicts (from top to bottom): 1. shooting a "cylindrical plug" into a sphere of "active material and some tamper"; 2. a "well tamped spheroid"; 3. pieces "mounted on a ring" with explosive material distributed around the ring, which when fired "the pieces would be blown inward to form a sphere"; 4. an "autocatalytic method" where the "active material is disposed in a hollow shell" with the hope of the reaction propagating inward (and thus improving its efficiency as it exploded); 5. another "autocatalytic method" whereby active material is contains "enough boron to make the mass just critical", and by adding more active material a reaction would start which would, as it proceeded, compress the boron and decrease its effectiveness at absorbing neutrons and thus increase the efficiency of the reaction. (Note that #4 and #5 were considered fairly speculative even in 1943 and were eventually disproven as feasible designs.)