Operation: WHITE SNARE

Operation: WHITE SNARE was a UNSC contingency plan, first drawn up in 2537 and prepared for in 2544, concerning the anticipated invasion of the core world Adrastos. In the event of a hostile planetary assault, fifteen high yield nuclear weapons sited at locations of tectonic instability across the planet's surface would be activated, destroying the colony along with anything on its surface.
Initially conceived as a plan to entice the Covenant into a large scale deployment on an uninhabited or sparsely populated UEG colony, it was ultimately decided that only a significant UEG world would be sufficient bait. This was because, firstly, any UNSC deception would not be convincing enough to create the illusion, when viewed from orbit, of a major target; and secondly, a less important colony would not guarantee a major Covenant attack, and would potentially expose WHITE SNARE to the enemy without optimum effectiveness. Several worlds were considered as the subject for WHITE SNARE, though Adrastos was eventually selected.
The use of a major colony such as Adrastos for such a destructive operation carried significant risk, however, and required the plan of drawing Covenant forces into an engagement to be revised. Rather than an active effort to attract the Covenant to the world, instead Operation WHITE SNARE became a contingency plan for the eventuality of Adrastos's invasion. Though the world's usefulness to the operation was its status as a significant colony, individuals or production plants vital to the war effort were relocated, and extensive plans were drawn up to extract UEG military and civilians from the world once the invasion had begun. Despite this, very few individuals beyond HIGHCOM knew of WHITE SNARE's existence, even up to and beyond the invasion itself.
In 2548, the Covenant did indeed invade Adrastos with a full scale planetary assault. The present UNSC Navy force, oblivious to the contingency operation, engaged and was destroyed by the Covenant Navy. Over the course of the two week engagement the UNSC were able to keep the most part of the Covenant force occupied on the ground, but were able to extract just a third of the civilians and military personnel on Adrastos's surface. At 1357 on 15 August, 2548, as Covenant assault carriers moved in to remove deployed forces, Operation: WHITE SNARE was initiated, resulting in the deaths of over 90% of those on the surface, Human and Covenant. The UNSC had scored a victory, though at a heavy, mostly self-inflicted, cost. The battle continued for three more days as UNSC vessels moved quickly to rescue survivors.
The success of Operation: WHITE SNARE later inform planning surrounding the SWAN SONG contingency.