Dahlgren gun
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The Dahlgren gun was a type of smoothbore cannon used by the US Navy prior to and during the Civil War.
Only the most primitive of cannon were cast in a single piece. Those made during the nineteenth century were made from many pieces of metal of various shapes and strengths to hold in a greater blast while being of the lightest possible weight.
John A. Dahlgren, head of the US Navy's gun development department, noticed that the greatest force of the blast was in the breech at firing, whereas when the projectile is near the end of the muzzle, it is much less. So he invented a cannon that was very thick at the breech, thin at the muzzle, and had a smoothed transition. This would be cheaper than a more advanced type. It was nicknamed the "bottle cannon" because it looked like a beer bottle, and was also nicknamed after him.
His design did not catch on with other navies, however. Improvements in charge and materials rendered his design obsolete before the twentieth century.
A weakness in this design was the small hoisting knob at the rear of the gun (which tended to break off) and the lack of an integral elevation setting mechanism. Both of these deficiencies were addressed by the evolution of this design, the Rodman gun.
