From Supreme Commander Wiki
Mobile Missile Launchers (often abbreviated to MML) are a class of units in Supreme Commander. They serve as T2 Indirect fire units for all the factions. Typically, they can inflict heavy damage at long range, with a high degree of accuracy because the missiles home in on their targets. MMLs, like TMLs, can be rendered less effective or ineffective in the presence of units possessing TMD.
MMLs are most useful in augmenting existing T1 armies to gain a large advantage over opposing T1 armies, being able to destroy most T1 units units in a single round from far away, as well as being able to out-range T1 PDs.
The four MMLs are: The Flapjack, the Viper, the Evensong, and the Ythisah