▁used ▁for ▁war ▁work , ▁including ▁computation ▁of ▁ball istic ▁tables , ▁B essel ▁tables ▁for ▁electron ics ▁and ▁other ▁applications , ▁and ▁calculations ▁used ▁by ▁the ▁Manh attan ▁Project ▁for ▁development ▁of ▁the ▁atomic ▁bomb . ▁ ▁Comp ilers ▁and ▁even ▁assemb lers ▁had ▁not ▁yet ▁been ▁invent ed , ▁so ▁all ▁programming ▁was ▁done ▁in ▁machine ▁code ▁p unch ed ▁into ▁paper ▁t ape . ▁Grace ▁Ho pper ▁called ▁Blo ch ▁the ▁Moz art ▁of ▁the ▁computer ▁due ▁to ▁his ▁ability ▁to ▁write ▁a ▁program ▁in ▁in k ▁and ▁have ▁it ▁run ▁the ▁first ▁time . ▁Robert ▁Campbell ▁called ▁Blo ch ▁the ▁primary ▁force ▁in ▁getting ▁the ▁Mark ▁I ▁into ▁product ive ▁operation . ▁ ▁Blo ch ▁and ▁Campbell ▁kept ▁not ebook s ▁in ▁which ▁they ▁wrote ▁out ▁pieces ▁of ▁code ▁that ▁had ▁been ▁checked ▁out ▁and ▁were ▁known ▁to ▁be ▁correct . ▁For ▁instance , ▁one ▁of ▁Blo ch ' s ▁rout ines ▁computed ▁s ines ▁for ▁positive ▁angles ▁less ▁than ▁ π / 4 ▁to ▁ 1 0 ▁digits . ▁Grace ▁Ho pper ▁just ▁copied ▁Blo ch ' s ▁routine ▁into ▁her ▁own ▁program ▁when ▁needed , ▁rather ▁than ▁using ▁the ▁( slow ) ▁s ine ▁unit ▁built ▁into ▁the ▁machine . ▁This ▁was ▁an ▁early ▁step ▁toward ▁the ▁creation ▁of ▁sub rout ines . ▁Later , ▁these ▁sub rout ines ▁were ▁stored ▁on ▁separate ▁paper ▁t ape ▁roll s , ▁although ▁branch ing ▁to ▁one ▁of ▁these ▁separate ▁paper ▁t apes ▁and ▁returning ▁to ▁the ▁main ▁program ▁was