Hunley was originally intended to attack by using a floating explosive charge with a contact fuse (a torpedo in 19th century terminology) which was towed at the end of a long rope.
Hunley was to approach an enemy ship on the surface, then dive under her, and surface again once beyond her.
The torpedo would be drawn against the targeted ship and explode.
This plan was discarded as dangerous because of the possibility of the tow line fouling Hunley's screw or drifting into the submarine herself.

Instead, a spar torpedo—a copper cylinder containing 135 pounds (61 kilograms) of black powder—was attached to a 22-foot (6.7 m)-long wooden spar, as seen in illustrations made at this time.
Mounted on Hunley's bow, the spar was to be used when the submarine was 6 ft (1.8 m) or more below the surface.
Previous spar torpedoes had been designed with a barbed point: the spar torpedo would be jammed in the target's side by ramming, and then detonated by a mechanical trigger attached to the submarine by a line, so that as she backed away from her target, the torpedo would set off.
However, archaeologists working on Hunley discovered evidence, including a spool of copper wire and components of a battery, that it may actually have been electrically detonated.
In the configuration used in the attack on Housatonic, it appears Hunley's torpedo had no barbs, and was designed to explode on contact as it was pushed against an enemy vessel at close range.
 After Horace Hunley's death, General Beauregard ordered that the submarine should no longer be used to attack underwater.
An iron pipe was then attached to her bow, angled downwards so the explosive charge would be delivered sufficiently under water to make it effective.
This was the same method developed for the earlier "David" surface attack craft used successfully against the USS New Ironsides.
The Confederate Veteran of 1902, printed a reminiscence authored by an engineer stationed at Battery Marshall who, with another engineer, made adjustments to the iron pipe mechanism before Hunley left on her last fatal mission on 17 February 1864.
A drawing of the iron pipe spar, confirming her "David" type configuration, was published in early histories of submarine warfare.
Hunley was originally intended to attack by using a floating explosive charge with a contact fuse (a torpedo in 19th century terminology) which was towed at the end of a long rope. Hunley was to approach an enemy ship on the surface, then dive under her, and surface again once beyond her. The torpedo would be drawn against the targeted ship and explode. This plan was discarded as dangerous because of the possibility of the tow line fouling Hunley's screw or drifting into the submarine herself.
Instead, a spar torpedo—a copper cylinder containing 135 pounds (61 kilograms) of black powder—was attached to a 22-foot (6.7 m)-long wooden spar, as seen in illustrations made at this time. Mounted on Hunley's bow, the spar was to be used when the submarine was 6 ft (1.8 m) or more below the surface. Previous spar torpedoes had been designed with a barbed point: the spar torpedo would be jammed in the target's side by ramming, and then detonated by a mechanical trigger attached to the submarine by a line, so that as she backed away from her target, the torpedo would set off. However, archaeologists working on Hunley discovered evidence, including a spool of copper wire and components of a battery, that it may actually have been electrically detonated. In the configuration used in the attack on Housatonic, it appears Hunley's torpedo had no barbs, and was designed to explode on contact as it was pushed against an enemy vessel at close range.  After Horace Hunley's death, General Beauregard ordered that the submarine should no longer be used to attack underwater. An iron pipe was then attached to her bow, angled downwards so the explosive charge would be delivered sufficiently under water to make it effective. This was the same method developed for the earlier "David" surface attack craft used successfully against the USS New Ironsides. The Confederate Veteran of 1902, printed a reminiscence authored by an engineer stationed at Battery Marshall who, with another engineer, made adjustments to the iron pipe mechanism before Hunley left on her last fatal mission on 17 February 1864. A drawing of the iron pipe spar, confirming her "David" type configuration, was published in early histories of submarine warfare.
H. L. Hunley (submarine)