From December 2 through December 10 the Halifax Amateur Radio Club will be holding a special event using the call CK100VDA to commemorate the Great Halifax Explosion of 1917. More information can be found here.
The explosion occurred on the morning of December 6, 1917, when a naval mishap set off a fire on the loaded munitions ship Mont Blanc. The explosion, which killed 2000 and leveled much of the city of Halifax, was the largest man-made explosion until the atomic age.
Fortunately, Boston was able to send a lot of aid quickly. Halifax sends Boston its official Christmas tree each year to mark the friendship between the two cities, and you can do the same by working CK100VDA this month.