Back in the day packs of cigarettes came with collectible cards - like the baseball cards some of you may remember from packs of chewing gum in more recent times. This series (there are dozens of them to browse here) featured the drum horses of various military groups, shown in all their parade finery. They were printed between 1908 and 1915.
Drum horses are large and calm-tempered, carrying the musician who play the large kettle drums in military parades. Though used sparingly now, they were formerly common, predominantly in Western Europe. They were not originally of any particular breed, though draft horses were commonly used to provide size and sturdiness.
Following on the recent popularity of the Gypsy Cob in the US, drum horses have gained new attention among fans of heavy horses. Organizations such as the Drum Horse Association are attempting to define a breed from the type, by allowing registration of horses carrying, for example, Clydesdale, Shire, Gypsy Cob and Friesian bloodlines. This site has some interesting and detailed background on the military history of drums and drum horses.