The Xindi launch platform with the Xindi test weapon inside
The Xindi launch platform was a small Xindi structure used to house the prototypes of the Xindi weapon prior to deployment.
In December 2153, the Xindi launch platform was in the Calindra system, for testing the second prototype weapon. (ENT: "Proving Ground")
Later, when Lorian spoke of his attempt to destroy the first probe, he explained to Captain Jonathan Archer that he "knew the coordinates of the launch platform, the exact minute the weapon was going to be deployed. But our plan didn't work." (ENT: "E²")
The launch platform was designed by John Eaves. At one point, it was called the "Xindi bomber". (Star Trek: The Art of John Eaves, pp.128–129)
The final draft script of "Proving Ground" referred to it as a "Xindi cargo vessel". That same teleplay additionally described the cargo vessel as "large", with "a port on its underside" which the script later referred to as a "launch port".