He had taken the weapon a long time ago. He was a warrior, after all, and a warrior was at his best when he had a weapon at his disposal for every situation.
He never actually thought he would have to use it, though.
The High Council was planning something. Truthfully, the High Council was always planning something, but he trusted those decisions less and less as each moment passed. If they were able to finally end the war, he knew the outcome would not be good. And so he was determined to do everything he could to halt the fighting on his own terms.
It was a routine trip in his Tardis that finally opened his eyes to what needed to be done.
The Time War may have been time-locked, but his trusty old Tardis could still move through space in an instant; she had long ago been decommissioned, but he would always have faith in her more than any other ship.
And for that reason, he did not understand the readings that came across his console when she rematerialized at the destination he had put in. They were supposed to be on Gallifrey. Indeed, according to his readings, they were at precisely the coordinates he had input, but the view screen and the sensor readings said differently. Outside of his Tardis there was…nothing.
The space where Gallifrey was supposed to be…where Gallifrey had once been…was empty. And she had left nothing in her wake. An entire planet…gone.
But this couldn't be right. Gallifrey could not have simply just disappeared without a trace. And of course it wasn't just Gallifrey; everything was gone. The entire Time War had disappeared.
He glared silently at the readings still being displayed on the console. No, this had to be wrong. With a new sense of determination, he input the coordinates once more and sent the Tardis through the vortex for a second time, again displacing himself from time ever so briefly.
When the Tardis rematerialized, he barely had time to blink before he was being knocked off his feet, courtesy of a blast of enemy fire just outside. Jumping to his feet he quickly confirmed what he knew must be true: the Time War and all of its participants had returned.
What had just happened?
None of this made sense. Gallifrey could not have simply disappeared, only to magically reappear moments later. There was no logical explanation for what had just happened.
What if he had somehow managed to get through the time lock? It should have been impossible, but this war was filled with so many things—so many horrible nightmares and travesties—that should have all been impossible. A tiny crack in a time lock was nothing. And trust his Tardis to be the one thing to get through it.
His pride in his most faithful companion was cut short as he made a greater realization, however.
Yes, he must have gotten through the time lock. But that meant that he had ended up in a time and place beyond the Time War; a time and place where Gallifrey did not exist. It was a sobering thought.
And yet it also brought illumination.
Gallifrey was gone…and so were the Daleks. There was no Time War. The never-ending bloodshed and death was done.
He did not want to admit that it was a thought that had always been just in the back of his mind: in a war of this magnitude, it was only inevitable that there could be no real winner. Everyone had to lose in order for the fighting to truly end once and for all. There could be no fighting, not now and not ever again. No more.
And that was when his mind finally turned to the Weapon. He had had it for so long and he had never intended to use it, but now it was the only way he could see to end the war.
He was not proud of his actions on that day…Gallifrey's last day. But it had to be done. Destroying Gallifrey allowed for the destruction of the Daleks, the Time War ended. It only took a single moment.
It is not until years later—more than a lifetime, really—that he discovered what actually happened to Gallifrey in that fateful moment when it disappeared from the sky, taking the entire Time War with it except for him. He had not actually found a crack in the Time Lock; the disappearance of Gallifrey had been the work of the High Council and their plot to win the war on their own nefarious terms. This discovery only served to reaffirm his belief that he had made the correct decision so long ago. He still did not have to like it, but it had been the right choice to finally use the weapon he had stolen. The Time Lords victorious was wrong.
And centuries later, when he was least expecting it, he was finally able to fully realize that he really had made the right choice, because Gallifrey was still out there. Somewhere beyond the reach of time and space, Gallifrey still existed, safe from destruction, safe within a single moment.