Very little threat.
An integral part of the U.S. strategy during the Civil War was the "Anaconda Plan" that called for the confederacy to basically be surrounded and strangled.
As part of this plan, the U.S. Navy implemented a blockade along the Confederate coastline, attempting to prevent the Confederacy to engage in trade. While the blockade was far from perfect, it was firme dup during the war and significantly hurt the Confederacy.
The Confederate Navy was never a big threat to the Union; the Confederacy having neither the manufacturing capability nor the raw materials for significant shipbuilding--especially as the age of the ironclad warship dawned. As such, the Confederacy's naval engagements were mainly defensive in nature.
The highlight of the war, in terms of naval significance, was the Battle of Hampton Roads between CSS Virginia (ex-USS Merrimack) and USS Monitor. This marked the first significant use of ironclad warhsips and rendered wooden, sail-powered vessels obsolete.
On a different note, knowing that they had no chance of standing against the might of the U.S. fleet, the Confederacy engaged heavily in commerge raiding, or guerre de course. Raiders such as CSS Alabama sunk numerous Union merchant ships in both the Pacific and Atlantic Oceans, damaging the U.S. economy. The Confederacy also issued a Letter of Marque to the first, and to this day only pirate submarine in history-Pioneer.
Riverine warfare; control of the rivers (like the Mississippi River).
By the word "posed," I assume you are asking about the kind of threat it posed towards the US Navy. "The C.S. Navy could never achieve equality with the Union Navy and used technological innovation, such as ironclads, submarines, torpedo boats, and naval mines (then known as torpedoes) to gain advantage over the Union Navy. In February 1861, the Confederate Navy had thirty ships, only fourteen of which were seaworthy, while the Union Navy had ninety vessels. The C.S. Navy eventually grew to 101 ships to meet the rise in naval conflicts and enemy threats."
Stephen Mallory
The Hunley sank with all hands after its attack.
Confederate States Navy was created in 1861.
Yes, submarines were used by the Confederate Navy in the US Civil War.
Stephen R. Mallory was the Confederate Secretary of the Navy. He was a major asset to the Southern cause with his imaginative ideas.
The Confederate capitol was moved to Richmond, VA. It's close proximity to Washington, DC, was a threat to the security of the US capital and ensured that a long and costly struggle between these two cities.
With Louisiana becoming a Confederate state, the Rebels were able to take over the US Mint in New Orleans and seizing US ordnance depots. The Rebels took control of the Phoenix Iron Works at Gretna, Louisiana and there they began to cast cannons for the soon to be Confederate navy.
Commander of the Confederate Army was Robert E. Lee.Secretary of the Confederate Navy was Stephen Mallory.
In Gretna, Louisiana the Phoenix Iron Works began to cast cannons for the upcoming Confederate navy. This was one of the few industrial companies that the South had.
merrimack monitor