The heroes, and sometimes the villains, in regency romances are often involved in war, whether in the Royal Navy, the army, or as spies. Even if their wartime activities do not appear directly in the story, their military experiences shape their lives and their characters. In the army, the most glamourous were the cavalry or the Guards regiments, and this was reflected in the higher costs of purchasing commissions in those regiments than in regiments of foot.
There were some army units in which commissions could not be bought—the engineers and the artillery. In both cases, cadets underwent the same basic training, including engineering (as you might expect!), chemistry and physics, and languages. On completion of basic training they could choose which branch to enter.