Repleetah's history is confusing -- there were two major battles fought there.
On 2646.080 the Kilrathi Empire attempted to take the Repleetah System as part of a counter-offensive responding to the Confederation's Epsilon Initiative. Bloody ground fighting, the worst so far in the war, ensued -- costing the Confederation 2.7 million soldiers and 1.2 million civilians -- and the Kilrathi over 7 million marines. The battle ended with a Confederate victory in 2651.290, although Kilrathi forces were still on the planet. *This* is the fighting we see on Wing Commander Academy -- after being wounded at Repleetah, Grunt joined the TCSNA's '54 class.
The more well-known fighting at Repleetah (presumably since it has some sort of moral message, or at least an interesting ending) started on 2654.287, when a group of human scientists attempted to make peaceful contact with a Kilrathi scientific group on the planet. Kilrathi forces responded with a full-scale biological attack. The CSF commander for the area ordered his forces to retreat -- and was decorated for his actions by Admiral Tolwyn. The TCMC reinforces Repleetah, but the Space Force refuses to assist in the fighting. A bloody trench-war, fought in bio-hazard suits, goes on for ten years -- during which time even the Marines stop sending reinforcements to Repleetah. It is during *this* time that Dekker is captured by the Kilrathi. In late 2664, Lt. Miles D'Arby leads his surviving soldiers in a final attempt to overrun the Kilrathi. No one survives.