Calavan was a British sniper during the events of Operation Morning Star.
Participating in the Anglo-American invasion of London, Calavan was posted in Alpha Company under the command of Captain Buckler. As part of Alpha Company, the unit was ordered to hold back Chimeran forces as members of Task Force Five planted demolition charges on Tower Bridge to prevent Chimeran Goliaths from pursuing the Anglo-American armored units.
As Chimeran forces began making pushes against Alpha Company, Calavan was able to survive the initial stages of the battle, often at times pushing the Chimera back temporarily. He also assisted in the destruction of the Stalker units that had arrived to reinforce the battered Chimeran forces. However, during the final part of the skirmish between Alpha Company and the Chimera, a Widowmaker appears.
As Captain Buckler drew the attention of the Widowmaker, he orders Calavan and Sgt. Nathan Hale to eliminate it. In the midst of doing so, Calavan is ambushed and killed by Hybrids, who storm his position. With Calavan dead, Hale is forced to eliminate the Widowmaker on his own, but not before Cpt. Buckler is killed, leaving him as the sole survivor.