In the morning hours of the day, it was a sepcial day. 3 Marine Corps Bases across the Imperial Mainland were taking part in an event that occurs every year. They open up to local schools, of whom bus students in for a day of education about the Military of the Empire and to learn what the Military does.
At 13:24, at two of the bases, warning sirents went off and everyone who worked there knew what it was. They started their evacuations into the multitude of underground bunkers on the bases in preparations that they were trained for. At one of the bases, though, not everyone got into the bunkers and were caught outside when each base was struck with a 10kt Nuclear Weapon.
It didn't take long for the Empire to find out who did it, and with the help of the International Community, those that were at fault were bought to justice.
That day, roughly 134 Children, 314 Marines and 400 Civilian Support Staff perished in an instant. Over the next couple years, space launches were stepped up by the Shazbotdom Imperial Space Administration and the Shazbotdom Marine Air Corps to put newly designed Sattelites into orbit to begin the building of a Missile Defence Shield.
Along with these, CGNs were purchased from shipyards across the world as mobile platforms for Anti-Ballistic Warfare to ensure that the trajedy would not be duplicated.