Ships built using 'Autodesign' (including AI ships) default to a missile rack size of 5. The rack size corresponds to the number of shots that the ship will get in combat. Five shots is often too many, as battles don't tend to last long enough to use all of those shots.
By applying this patch, you may choose an alternate number to use. The recommendation is for 3, but you may choose any number you prefer.
NOTE: This patch is superceded by the Autobuild patch. They are not incompatible (ie, you may have both installed without creating conflicts), but if the Autobuild patch is installed, this one will not function.