  A pp-wave solution to 11-dimensional supergravity is given with precisely 26
supercharges. Its uniqueness and the absence of 11-dimensional pp-waves which
preserve (precisely) 28 or 30 supercharges is discussed. Compactification on a
spacelike circle gives a IIA configuration with all 26 of the supercharges. For
this compactification, D0 brane charge does not appear in the supersymmetry
algebra. Indeed, the 26 supercharge IIA background does not admit any
supersymmetric D-branes. In an appendix, a 28 supercharge IIB pp-wave is
presented along with its supersymmetry algebra.
