It is used by both armies and navies, but navies use it in larger masses, fired in more powerful guns.
Of course this does not mean that it would be impossible to send a lot of powder to a fort, more than a fleet could carry, and fire it; but it does mean that history shows that forts have rarely been called upon to fire much powder, that their lives have been serene, and that most of the powder fired on shore has been fired by infantry using muskets--though a good deal has been fired by field and siege artillery.
Leaving forts out of consideration and searching for something else in which to use gunpowder on a large scale, we come to siege-pieces, field-pieces, and muskets.

Disregarding siege-pieces and field-pieces, for the reason that the great variety of types makes it difficult to compare them with navy guns, we come to muskets.
Now the musket is an extremely formidable weapon, and has, perhaps, been the greatest single contributor to the victory of civilization over barbarism, and order over anarchy, that has ever existed up to the present time.

But the enormous advances in engineering, including ordnance, during the last fifty years, have reduced enormously the relative value of the musket.

Remembering that energy, or the ability to do work, is expressed by the formula: E=1/2 MV^2, remembering that the projectile of the modern 12-inch gun starts at about 2,900 f.s.velocity and weighs 867 pounds, while the bullet of a musket weighs only 150 grains and starts with a velocity of 2,700 feet per second, we see that the energy of the 12-inch projectile is about 47,000 times that of the bullet on leaving the muzzle.

But after the bullet has gone, say 5,000 yards, its energy has fallen to zero, while the energy of the 12-inch projectile is nearly the same as when it started.
While it would be truthful, therefore, to say that the energy of the 12-inch gun within 5,000 yards is greater than that of 47,000 muskets, it would also be truthful to say that outside of 5,000 yards, millions of muskets would not be equal to one 12-inch gun.
Not only is the 12-inch gun a weapon incomparably great, compared with the musket, but when placed in a naval ship, it possesses a portability which, while not an attribute of the gun itself, is an attribute of the combination of gun and ship, and a distinct attribute of naval power.