They were popular for use as long range guns to harass or snipe at the enemy. Infantry actually used them to some extent. Artillery units would use them and they used them aboard ships at the time too. But when you had fortifications for a siege, then the guns could fire on the enemy positions and they couldn't fire back unless they had some too. I would not be surprised if some of the forts at the time had the guns for use as well. Several American generals or leaders had the big wall or fortress guns made for them. The British forts likely had some within for their usage too. The British actually issued the guns to their various military units.