A bit late but, here we go...
Using the tragedy of Junius Seven as justification, a number of PLANT Supreme Council councilors, including Patrick Zala, pushed for the eployment of Neutron Jammers on Earth and justify it as prevention of Alliance nuclear attack. Although the then-Supreme Council Chairman Siegel Clyne is reluctant, the majority support for N-Jammer deployment was large enough that he had to authorize the deployment as part of Operation Ouroboros.
On April 1st, a ZAFT fleet arrived on Earth orbit and engaged the Alliance forces there. Despite the Earth Alliance's best efforts, they could not stop the deployment, many of the craft broke through the atmosphere and launched the N-Jammers into the Earth. Causing energy crisis as nuclear powerplants shut down.
Certain unconfirmed records indicated that Rau le Creuset and Mu la Flaga engaged each other for the first time during the battle, although only briefly, with neither side giving much thought to each other.