This paper examines the necessity of including ion viscosity in modeling laser fusion implosions. Using the Naval Research Laboratory one-half Mega Joule laser fusion target as an example, it is shown that for virtually the entire implosion up to maximum compression, and the entire rebound after the implosion, ion viscosity is unimportant. However for about half a nanosecond before peak implosion, ion viscosity can have a significant, but by no means dominant effect on both the one-dimensional flow and on the Rayleigh-Taylor instability.
