J. von Neumann, H.H. Goldstine, Numerical Inverting of Matrices of High Order, Bull. Amer. Math. Soc., Vol. 53, No. 11, pp. 1021-1099, 1947.
According to KJ. VuikGrcar, Birthday of Modern Numerical Analysis, available here or here, this paper is considered the first paper in modern analysis because it is the first to study rounding error and because much of the paper is an essay on scientific computing (albeit with an emphasis on numerical linear algebra).

