"For a few weeks in 1861 Britain was on the verge of war with the United States. After two Confederate commissioners were seized from the British mail packet ‘Trent’ by a US ship, Britain was incensed and began to send British regulars to support troops in Canada already out there.
The crisis became known as the Tent Affair or the Trent Crisis. Two battalions of Guards actually landed in Canada, with the third to follow, which shows the concern and outrage the British government felt over the crisis.
It seems like these would have been part of the 75,000 British regulars and potentially 50,000 Canadian militia and volunteers, ready to march. Of course in a matter of several weeks the crisis was over, but 18,000 British regulars (6,823 re-enforcements sent during the crisis) were on active service in Canada by early ’62."
Source: Perry Miniatures